ii;ili:u:i I ; I ! I r : I r I liiii iiiiiiii; THE STRUCTURE AND DEVELOPMENT OF MOSSES AND FERNS fl^^^ a9 "* o The Structure and Development of Mosses and Ferns i^Archegoniatae) THIRD EDITION, REVISED AND ENLARGED BY DOUGLAS HO'UQHTON CAMPBELL, Ph.D. Professor of Botany LfiwAnd Stanford Jjnior UnfvejvSity ■J < t) •' '^ * 1 » .^ .J - . ^' • - . THE MACMILLAN COMPANY London : Macmillan & Co., Ltd. 1918 All ri^hfs reserved ;^/r Copyright, 1905 By the MACMILLAN COMPANY ^ w ■* * >* ► < c ( •« ^ • • < / Srt up ^rM ere(?trotyir<^a , ' / ' Published, September, looi , , \ Rep'-in^^ed JuV. 1913 ' . - '^< c PREFACE TO THE SECOND EDITION Since the first edition of the present work was pub- lished, the number of important investigations on the struc- ture and development of the Archegoniatse has been so great that it has been found necessary to recast entirely certain portions of the work, this being especially the case with the chapters dealing with the eusporangiate Ferns. The whole book, however, has been carefully revised, and a good deal of new matter introduced, including two special chapters on the geological history of the Archegoniates, and the significance of the alternation of generations. Some of the new material incorporated in the present work is published for the first time; but much of it is based upon papers published by the writer since the first edition was published. The work of other investigators has been freely drawn upon, and acknowledgment has been made in all cases where statements or illustrations have been bor- rowed from other sources than the writer's own inves- tigations. The large number of recent books and papers on the Archegoniates has involved an entire revision of the bibli- ography, which has been materially augmented. It is hoped that it will be found to be a fairly complete list of the more recent works bearing upon the structure of the Archegoniates. The results of more recent investigations have necessi- tated, in some cases, a modification of certain views ex- pressed by the author in the earlier edition. In other cases, however, his views have been confirmed as the result of more complete knowledge of certain forms. PREFACE In view of the decidedly unsettled state of nomenclature at the present time, it has seemed best to maintain a some- what conservative attitude in this matter, and this will ex- plain the retention of some familiar names, which perhaps are not in accord with a strict law of priority. The author is especially indebted to Professor E. C. Jeffrey and to Dr. W. R. Shaw, for valuable preparations which were of great assistance in the preparation of the chapters on the Ferns. Thanks are also due one of my students, Mr. H. B. Humphrey, for the preparation of the drawings for figures 43, 44 and 47. The author also would express his thanks to Professor D. S. Johnson of Johns Hopkins University for kindly re- vising a portion of the bibliography, and to Professor G. J. Peirce of Stanford University for valuable assistance in reading part of the proof. DOUGLAS HOUGHTON CAMPBELL. Stanford University, April, 1905. VI PREFACE TO THE THIRD EDITION In the second edition of the "Mosses and Ferns," the original text was carefully revised, and a good deal of it was rewritten. At the same time considerable new matter was added. In preparing the present edition of the book, it has not seemed necessary to change the body of the text, the new material being given in the form of an appendix. Since the publication of the last edition, as might be expected, numerous contributions have been made to the literature of the Morphology and Classification of the Archegoniates. Among these contributions are several publications by the writer. These are for the most part based upon collections of tropical Liverworts and Ferns made by the writer, including some new and rare species of the Indo-Malayan region. A summary of the more important results of these studies as well as those of other investigators is added to the text in the form of an appendix, in which the new material is arranged under the Chapter headings which deal with the allied topics in the main text. In the appendix, also, certain errors of state- ment and reference in the original text have been corrected. The numerous additions in the literature on the subject have necessitated a complete revision of the bibliography, which has been very considerably enlarged. It is hoped that with the appendix and augmented bibliog- raphy the book will prove a satisfactory statement of our present knowledge of the structure and development of the Archegoniate Plants. DOUGLAS HOUGHTON CAMPBELL. Stanford University, January, 1918. vu CO NTENTS CHAPTER I Introduction = i CHAPTER H MusciNE^ (Bryophyta) — Hepatic^ — Marchantiales 8 CHAPTER HI The Jungermanniales 72 CHAPTER IV The Anthocerotes » « o . . . 120 CHAPTER V The Mosses (Musci) : Sphagnales — Andre^eales 160 CHAPTER VI The Bryales • , 188 CHAPTER VII The Pteridophyta — Filicine^ — Ophioglossace^ 229 CHAPTER VIII Marattiales ^JZ CHAPTER IX FiLiciNE^ Leptosporangiat^ 305 CHAPTER X The Homosporous Leptosporangiat^ (Filices) 346 CHAPTER XI Leptosporangiat^ Heterospore^ ( Hydro pterides) 396 CHAPTER XII Equisetine^ 443 CHAPTER XIII Lycopodine^ 483 CHAPTER XIV Isoetace^ 536 CHAPTER XV The Nature of the Alternation of Generations 562 CHAPTER XVI Fossil Archegoniates 576 CHAPTER XVII Summary and Conclusions 592 ix CONTENTS Appendix 607 Bibliography 645 Index 681 CHAPTER I INTRODUCTION Under the name Archegoniatse are included a large number of plants which, while differing a good deal in many structural details, still agree so closely in their essential points of structure and development as to leave no room for doubting their close relationship. Besides the Bryophytes and Pteri- dophytes, which are ordinarily included under this head, the Gymnospermse or Archespermge might very properly be also embraced here, but we shall use the term in its more restricted meaning. The term Archegoniat^e has been applied to these plants because the female reproductive organ or archegonium is closely alike, both in origin and structure, in all of them. This is a multicellular body, commonly flask-shaped, and either entirely free or more or less coherent with the tissues of the plant. In all cases there is an axial row of cells developed, of which the lowxst forms the egg. The others become more or less completely disorganized and are discharged from the archegonium at maturity. Among the Algae there is no form at present known in which the female organ can be certainly compared to the archegonium, although the oogonium of the Characese recalls it in some respects. The antheridium or male organ of the Archegoniatse, while it shows a good deal of similarity in all of them, still exhibits much more variation than does the archegonium, and is more easily comparable with the same organ in the Algae, especially the Characese. Like the archegonium it may be entirely free, or even raised on a long pedicel ; or it may be completely sunk in the tissue of the plant, or even be formed endogenously. It usually consists of a single outer layer of cells containing 2 MOSSES AND FERNS chap. chlorophyll, and these enclose a mass of small colourless cells, the sperm cells, each of which gives rise to a single ciliated spermatozoid. The development of the latter is very uniform throughout the Archegoniatse, and differs mainly from the same process in the higher green Algae, especially the Characeae, in the larger amount of nuclear substance in the spermatozoids of the former. Fertilisation is only effected when the plants with ripe sexual organs are covered with water. The absorption of water by the mature sexual organs causes them to open, and then, as the spermatozoids are set free, they make their way through the water by means of their cilia and enter the open archegonium, into which they penetrate to the egg. The sexual cells do not differ essentially from those of the higher Algae, and point unmistakably to the origin of the Arche- goniatae from similar aquatic forms. Indeed all of the Archegoniatae must still be considered amphibious, inasmuch as the gametophyte or sexual plant is only functional when partially or completely submerged. Non-sexual gonidia are known certainly only in Aneura, one of the lower Liverworts, but special reproductive buds or gemmae, both unicellular and multicellular, are common in many forms. A very marked characteristic of the whole group is the sharply-marked alternation of sexual and non-sexual stages. The sexual plant or gametophyte varies much in size and complexity. It may be a simple flat thallus comparable in structure to some Algae, and not superior to these in com- plexity so far as the vegetative parts are concerned. In others it becomes larger and shows a high degree of differentiation. Thus among the Liverworts the Marchantiaceae, while the gametophyte still retains a distinctly thalloid form, still show a good deal of variety in the tissues of which the thallus is composed. In others, e.g., the true Mosses, the gametophyte has a distinct axis and leaves, and in the higher ones the tissues are well differentiated for special functions. The gametophyte itself may show two well-marked phases, the protonema and the gametophore. The former is usually filamentous, and arises directly from the germinating spore; and upon the protonema, as a special branch or bud, the much more complex gametophore is borne. Often, however, as in many thallose I INTRODUCTION 3 Liverworts and Pteridophytes, the protonema is not clearly distinguishable from the gametophore, or may be completely suppressed. In the Pteridophytes the gametophyte is, as a rule, much simpler than in the Bryophytes, resembling most nearly the less specialised forms of the latter. In the so-called heterosporous Pteridophytes the gametophyte becomes ex- tremely reduced and the vegetative part almost entirely sup- pressed, and its whole cycle of development may, in extreme cases, be completed within twenty- four hours or even less. The non-sexual generation, or "sporophyte," arises normally from the fertilised Qgg, but may in exceptional cases develop as a bud from the gametophyte. In its simplest form all the cells of the sporophyte, except a single layer upon the out- side, give rise to spores, but in all the others there is developed a certain amount of vegetative tissue as well, and the sporo- phyte becomes to a limited extent self-supporting. In the higher Bryophytes the sporophyte sometimes exceeds in size the gametophyte, and develops an elaborate assimilative system of tissues, abundantly supplied wnth chlorophyll and having an epidermis with perfect stomata; but even the most complex moss-sporogonium is to a certain extent dependent upon the gametophyte with which it remains in close connection by means of a special absorbent organ, the foot. In these highly developed sporogonia the sporogenous tissue occupies but a small space, by far the greater part of the tissue being purely vegetative. In the Pteridophytes a great advance is made in the sporo- phyte beyond the most complex forms found among the Bryophytes. This advance is twofold, and consists both in an external differentiation and a more perfect development of the tissues. The earliest divisions of the embryo resemble very closely those of the Bryophyte sporogonium, but at an early stage four distinct organs are usually plainly distinguishable, viz., stem, leaf, root, and foot. The last corresponds in some degree to the same organ in the moss-sporogonium, and like it serves as an absorbent organ by which the young sporophyte is supplied with nourishment from the gametophyte. In short, the young sporophyte of the Pteridophyte, like that of the Bryophyte, lives for a time parasitically upon the gametophyte. Sooner or later, however, the sporophyte becomes entirely independent. This is effected by the further growth of the 4 MOSSES AND FERNS chap. primary root, which brings the young sporophyte into direct communication with the earth. The primary leaf, or cotyle- don, enlarges and becomes functional, and new ones arise from the stem apex. Usually by the time this stage is reached the gametophyte dies and all trace of it soon disappears. In some of the lower forms, however, the gametophyte is large and may live for many months, or even years, when not fecundated, and even when the sporophyte is formed, the prothallium (gametophyte) does not always die immediately, but may remain alive for several months. The spore-forming nature of the sporophyte does not manifest itself for a long time, sometimes many years, so that spore-formation is much more subordinate than in the highest Bryophytes. With few exceptions the spores are developed from the leaves and in special organs, sporangia. In the simplest case, e. g., Ophio- glossum, the sporangia are little more than cavities in the tissue of the sporiferous leaf, and project but little above its surface. Usually, however, the sporangia are quite free from the leaf and attached only by a stalk. These sporangia are in the more specialised forms of very peculiar and characteristic structure, and are of great importance in classification. Corresponding to the large size and development of special organs in the sporophyte of the Pteridophytes, there is a great advance in the specialisation of the tissues. All of the forms of tissue found in the Spermaphytes occur also among the Pteridophytes, w^hich indeed, so far as the character of the tissues of the sporophyte is concerned, come much nearer to the former than they do to the Bryophytes. This is especially true of the vascular bundles, which in their complete form are met with first in the sporophyte of the Pteridophyta. In size, too, the sporophyte far exceeds that of the highest Mosses; w^hile in these the sporogonium seldom exceeds a few centime- tres in extreme height, in some Ferns it assumes tree-like pro- portions with a massive trunk lo to 15 metres in height, with leaves 5 to 6 metres in length. In the formation of the spores all of the Archegoniatse show great uniformity, and this extends, at least as regards the pollen spores, to the Spermatophytes as well. In all cases the spores arise from cells which at first form a solid tissue arising from the division of a single primary cell, or group of cells (Archesporium). These cells later become more or less I INTRODUCTION 5 completely separated, and each one of these so-called "spore mother cells," by division into four daughter cells, forms the spores. The young spores are thin walled, but later the wall becomes thicker and shows a division into two parts, one inner layer, which generally shows the cellulose reaction and is called the endospore (intine), and an outer more or less cuticularised coat, the exospore (exine). In addition a third outer coat (perinium, epispore) is very generally present. As the spore ripens there is developed within it reserve food materials in the form of starch, oil, and albuminous matter, and quite frequently chlorophyll is present in large quantity. Some spores retain their vitality but a short time, those of most species of Equisetum and Osiminda, for example, germinating with difficulty if kept more than a few days after they are shed, and very soon losing their power of germination com- pletely. On the other hand, some species of Marsilia have spores so tenacious of life that they germinate perfectly after being kept for several years. From the germinating spore arises the gametophyte bear- ing the sexual organs. Both archegonia and antheridia may be borne upon the same plant, or they may be upon separate ones. From the fertilised egg within the archegonium is pro- duced the sporophyte or non-sexual generation, and from the spores which it produces arise the sexual individuals again, thus completing the cycle of development. On comparing the lower Archegoniates with the higher ones, it is at once evident that the advance in structure consists mainly in the very much greater development of the sporophyte. In the Bryophytes, as a class, the gametophyte is more impor- tant than the sporophyte, the latter being, physiologically, merely a spore-fruit, which in many forms, e. g., Sphagnum, is of relatively rare occurrence. The gametophyte in such forms is perennial, and the same plant may produce a large number of sporogonia, and at long intervals. The sporophyte in such forms is small and simple in structure, and its main function is spore formation, as it has but little power of independent growth. In the Pteridophytes, on the other hand, the gameto- phyte (prothallium) rarely produces more than one sporophyte, and as soon as this, by the formation of a root and leaf, becomes self-supporting, the gametophyte dies. In short, the sole 6 MOSSES AND FERNS chap. function of the latter in most of them is to support the sporo- phyte until it can take care of itself. When the lower Pteridophytes are compared with the more specialised ones, a similar difference is found. In the lower forms, like the Marattiacese and Equisetacese, the gametophyte is relatively large and long-lived, and closely resembles certain Liverworts. In these forms a considerable time elapses before sexual organs are produced, and in artificial cultures of the Marattiacese a year or more sometimes passes before archegonia are formed. These prothallia, too, multiply by budding, much as the Liverworts do. In case no archegonia are fecundated the prothallium may grow until it reaches a length of three or four centimetres, and resembles in a most striking manner a thallose Liverwort. In such large prothallia it is not unusual for more than one archegonium to be fecundated, although usually only one of the embryos comes to maturity, and the prothallium may continue to live for some time after the sporophyte has become independent. Usually, however, as soon as an archegonium is fertilised, the formation of new ones ceases, and as soon as the sporophyte is fairly rooted in the ground the prothallium dies. In most of the lower Pteridophytes the prothallia are monoecious, but in the more specialised ones are markedly dioecious. When this is least marked the males and females differ mainly in size, the latter being decidedly larger; in the more extreme cases the difference is much more pronounced and is correlated with a great reduction in the vegetative part of the gametophyte of both males and females. This reaches its extreme phase in the so-called heterosporous forms. In these the sex of the gametophyte is already indicated by the character of the spore. Two sorts of spores are produced, large and small, which produce respectively females and males. In all of the heterosporic Pteridophytes the reduction of the vege- tative part of the gametophyte is very great, especially in the male plants. Here this may be reduced to a single quite functionless cell, and all the rest of the plant is devoted to the formation of the single antheridium. In the female plants the reduction is not so great; and although sometimes but one archegonium is formed, there may be in some cases a consider- able number, and owing to the large amount of nutritive material in the spore, in case an archegonium is not fertilised. I INTRODUCTION 7 the prothallium, even if it does not form chlorophyll, may grow for a long time at the expense of the food materials that nor- mally are used by the developing embryo. In strong contrast to the slow growth and late development of the reproductive organs in the homosporous forms, most of the heterosporous Pteridophytes germinate very quickly. The Marsiliacese, in which the female prothallium is extremely reduced, show the opposite extreme. Here the whole time necessary for the germination of the spores and the maturing of the sexual organs may be less than twenty- four hours, and within three or four days more the embryo is completely developed. That heterospory has arisen independently in several widely separated groups of Pteridophytes is plain. The few genera that still exist are readily separable into groups that have comparatively little in common beyond possessing two sorts of spores; but each of these same forms shows much nearer affinities to certain widely separated homosporous groups. In some of the heterosporous forms the first divisions in the germinating spore take place while it is still within the sporan- gium, and may begin before the spore is nearly fully devel- oped. In other cases the sporangia become detached when ripe, and the spore (or spores), still surrounded by the spo- rangium, falls away from the sporophyte before germination begins. In these respects the heterosporous Pteridophytes show the closest analogy with the similar processes among the lower Spermatophytes, where it has been shown in the most conclusive manner that the ovule with its enclosed embryo-sac is the exact morphological equivalent of the macrosporangium of Selaginella or Azolla, for example, and that the seed is simply a further development of the same structure. CHAPTER II MUSCINAE (BRYOPHYTA)— HEPATICAE— MARCHANTIALES The first division of the Archegoniatse, the Muscinese or Bryophyta, comprises the three classes, Hepaticse or Liverworts, the Musci or Mosses and the Anthocerotes. In these as a rule the gametophyte is much more developed than the sporophyte, and indeed in many forms the latter is very rarely met with. They are plants of small size, ranging in size from about a milli- metre in length to 30 centimetres or more. A few of them are strictly aquatic, i. e., Riella and Ricciocarpiis among the Hepat- icse, and Fontinalis of the Mosses; but most of them are terrestrial. A favourite position for many is the trunks of trees or rocks. Many others grow upon the earth. They vegetate only when supplied with abundant moisture, and some forms are very quickly killed if allowed to become dry; but those species which grow in exposed places may be com- pletely dried up without suffering, and some of those that inhabit countries where there are long dry periods may remain in this condition for months without losing their vitality, reviving immediately and resuming growth as soon as they are supplied with the requisite moisture. The germinating spores usually produce a more or less well-marked "protonema," from which the gametophore arises secondarily. The protonema sometimes is persistent and forms a dense conferva-like growth, but more commonly it is transient and disappears more or less completely after the gametophore is formed. No absolute line, however, can be drawn between protonema and gametophore, as the former may arise secondarily from the latter, or even from the sporo- phyte. With very few exceptions, e.g., Buxhaiimia, the game- tophyte of the Muscinese is abundantly supplied with chloro- 8 CH. II MUSCINE^— HEPATIC.^— MARCH ANTI ALES 9 phyll, and therefore capable of entirely independent growth. No true roots are found, but rhizoids are generally present in great numbers, and these serve both to fasten the plant to the substratum and also to supply it with nutriment. The form of the gametophyte varies much. In the simplest Hepaticas, like Anciira and Pcllia, it is a flat, usually dichoto- mously branched thallus composed of nearly or cjuite uniform cells, without traces of leaves or other special organs. From this simplest type, which is quite like certain Algse, differentia- tion seems to have proceeded in two directions; in the first instance the plant has retained its thallose character, but there has been a specialisation of the tissues, as we see in the higher Marchantiaceae. In the second case the differentiation has been an external one, the thallose form giving place to a dis- tinct leafy axis. This latter form reaches its completest expression in the higher Mosses, where it is accompanied by a high degree of specialisation of the tissues as well. The growth is usually from a single apical cell, which varies a good deal in form among the thallose Hepaticse, but in the foliose Hepaticse and Mosses is with few exceptions a three-sided pyramid. The gametophyte of the Muscinese frequently is capable of rapid multiplication, w^hich may occur in several ways. Where a filamentous protonema is present this branches extensively, and large numbers of leafy axes may be produced as buds from it. Sometimes these buds are arrested in their development and enter a dormant condition, and only germinate after a period of rest. Another very common method of multiplica- tion is for the growing ends of the branches of a plant to become isolated by the dying aw^ay of the tissues behind them, so that each growing tip becomes the apex of a new plant. Very common in the Hepatic?e, but less so in the Mosses, is the formation of gemmae or special reproductive buds. These are produced in various ways, the simplest being the separation of single cells, or small groups of cells, from the margins of the leaves. In the case of Aneura midtifida they are formed within the cells and discharged in a manner that seems to be identical with that of the zoospores of many Algae. Again, multicellu- lar gemmae of peculiar form occur in several of the Hepaticae, e.g., Blasia, Marchantia, wdiere they occur in special receptacles, 10 MOSSES AND FERNS chap. and amonr the Mosses similar ones are common in Tetraphis and some other genera. The archegonia of all the Muscineae agree closely in their earlier stages, but differ more or less in the different groups at maturity. In all cases the archegonium arises from a single superficial cell, in which three vertical walls are formed that intersect so as to form an axial cell and three peripheral ones. From the axial cell develop the &gg, canal cells, and cover cells of the neck, and from the peripheral cells the wall of the venter and the outer neck cells. In all Muscineae except the Antho- cerotes the archegonium mother cell projects above the sur- rounding cells, but in the latter the mother cell does not project at all, and the archegonium remains completely sunken in the thallus. In all other forms the archegonium is nearly or quite free, and usually provided with a short pedicel. This is espe- cially marked in the Mosses, where the lower part of the arche- gonium is as a rule much more massive than in the Hepaticae. The most marked difference, however, between the arche- gonium of the Hepaticse and Mosses is in the history of the cover cell or uppermost of the axial row of cells of the young archegonium. This in the former divides at an early period into four nearly equal cells by vertical walls, the resulting cells either remaining undivided, or undergoing one or two more divisions ; but in the Mosses this cell functions as an apical cell, and to its further growth and division nearly the whole growth of the neck is due. The antheridia, except in the Anthocerotes, also arise from single superficial cells, and while they differ much in size and form, are alike in regard to their general structure. The antheridium always consists of two parts; a stalk or pedicel, which varies much in length, and the antheridium proper, made up of a single layer of superficial cells and a central mass of small sperm cells. The former always contain chloroplasts, which often become red or yellow at maturity. The sperm cells have no chlorophyll, but contain abundant protoplasm and a large nucleus, which latter forms the bulk of the body of the spermatozoid found in each sperm cell of the ripe antheridium. The spermatozoids are extremely minute filiform bodies, thicker behind and provided with two fine cilia attached to the forward end. Adhering to the thicker posterior end there may usually be seen a delicate vesicle, which represents the II MUSCINEAi—HEPA TIC^— MARCH ANTI ALES ii remains of the cell contents not used up in the formation of the spermatozoid. When the ripe sexual organs are placed in water their outer cells absorb water rapidly and become strongly distended, while the central cells, i.e., the canal cells of the archegonium, and the sperm cells, whose walls have become mucilaginous, have their walls dissolved. The swelling of the mucilage derived from the walls of the central cells, combined with the pressure of the strongly distended outer cells, finally results in the bursting open of both archegonium and antheridium. In the former, by the forcing out of the remains of the canal cells an open channel is left down to the ^gg, which has been formed by the contracting of the contents of the lowest of the axial cells. In the antheridium the walls of the sperm cells are not usually completely dissolved at the time the anther^ idium opens, so that the spermatozoids are still surrounded by a thin cell wall when they are first discharged. This soon is completely dissolved, and the spermatozoid then swims away. The substance discharged by the archegonium exer- cises a strong attraction upon the spermatozoids, which are thus directed to the open mouth of the archegonium, which they enter. Only a single one actually enters the Qgg, w^here it fuses with the egg-nucleus, and thus effects fertilisation. The tgg immediately secretes a cellulose wall about itself, and shortly after the fusion of the nuclei is complete the first segmentation of the young embryo takes place. The origin of the sexual organs is from a single cell, but the position of this cell varies much. In the thallose Hepaticas it is a superficial cell, formed from a segment of the apical cell either of a main axis or of a special branch. In most of the foliose Hepaticse and the Mosses, the apical cell of the shoot becomes itself the mother cell of an archegonium, and of course with this the further growth of the axis is stopped. The antheridia in the foliose Hepatic?e are usually placed singly in the axils of more or less modified leaves, but in most Mosses the antheridia form a terminal group. ]\Iixed with the sexual organs are often found sterile hair-like organs, paraphyses, often of very characteristic forms. In the foliose Hepaticse and most Mosses, the archegonia are often surrounded by specially modified leaves, and in the former there is also an inner cup-like perichastium formed from the tissue surrounding 12 MOSSES AND FERNS chap. the archegonia. In the thallose Hepaticae, both antheridia and archegonia are generally enclosed by a sort of capsule, similar to the perichsetium of the foliose forms formed by the growth of the tissue of the thallus immediately surrounding them. The Asexual Generation {Sporophyte, Sporophore, Sporogonium) The sporophyte of the Muscinese is usually known as the sporogonium, and, as already stated, never becomes entirely independent of the gametophyte. After the first divisions are completed there is at an early period, especially in the Hepaticse, a separation of the spore-producing tissue or arche- sporium, all the cells of which may produce spores, as in Riccia and the Mosses, or a certain number form special sterile cells which either undergo little change and serve simply as nourish- ment for the growing spores, as in Sphccrocarpus, or more commonly assume the form of elongated cells, — elaters, which assist in scattering the ripe spores. Classification Class I. Hepaticce {Liverworts) The protonema is either rudimentary or wanting, and usually not sharply differentiated from the gametophore. The gametophore is, with the exception of Haplomitrium and Calo- hryum, strongly dorsi ventral, and may be either a (usually dichotomously) branched thallus or a stem with two or three rows of leaves. Non-sexual multiplication of the gametophyte by the separation of ordinary branches, or by special reproduc- tive bodies, gonidia (Aneiira multiUda) or gemmae — (many foliose Jungermanniaceae, Blasia, Marchantia, etc.). The sporogonium (except in Anthocerotes) remains within the enlarged venter (calyptra) of the archegonium until the spores are ripe. Before the spores are shed the sporogonium generally breaks through the calyptra by the elongation of the cells of the stalk or seta. All the cells of the archesporium may produce spores, or part of them may produce sterile cells or elaters. II MUSCINEAi— HEPATIC JE— MARCH ANTI ALES 13 Class II. Anthoccrotcs. Gametophyte, a simple thallus, or sometimes showing a trace of leaf-formation in Dcndroccros; a single large chloro- plast, containing a pyrenoid, in each cell ; archegonium sunk in the thallus, the antheridium endogenous; sporophyte large, with long continued basal growth ; sporogenous tissue derived from the outer tissue (amphithecium) of the embryo. Class III. Miisci (Mosses) The gametophyte shows a sharp separation into protonema and gametophore. The protonema arises primarily from the germinating spore, and may be either a flat thallus or more commonly an extensively branching confervoid growth. Upon this as a bud the gametophore arises. This has always a more or less developed axis about w^hich the leaves are arranged in two, three, or more rows. A bilateral arrange- ment of the leaves is rare, and the stems branch monopodially. The asexual multiplication is by the separation of branches through the dying away of the older tissues, or less commonly by special buds or gemmse. Both stem and leaves have the tissues more highly differentiated than is the case in the Hepaticse. The archesporium is developed as a rule later than is the case in the Hepaticse, and within is a large central mass of tissue, the columella, which persists until the capsule is ripe. In most cases there is a large amount of assimilative tissue in the outer part of the capsule, and the epidermis at its base is provided with stomata. The growing embryo breaks through the calyptra at an early stage, and the upper part is in most cases carried up on top of the elongating sporogonium. In very much the greater number of forms the top of the cap- sule comes away as a lid (operculum). THE HEPATIC^ The Hepaticai show many evidences of being a primitive group of plants, and for this reason a thorough knowledge of their structure is of especial importance in studying the origin of the higher plants, as it seems probable that all of these are derived from Liverwort-like forms. On comparing the 14 MOSSES AND FERNS chap. Hepaticse with the Mosses one is at once struck with the very much greater diversity of structure shown by the former group, although the number of species is several times greater in the latter. On the one hand, the Hepaticse approach the Algae, the thallus of the simpler forms being but little more compli- cated than that of many of the higher green Algae. On the other hand, these same simpler Liverworts resemble in a most striking manner the gametophyte of the Ferns. The same difference is observed in the sporophyte. This in the simplest Liverworts, e. g., Riccia, is very much like the spore-fruit of Coleochccfe, one of the confervoid green Algge ; on the other hand, the sporogonium of Anthoceros shows some most significant structural affinities with the lower Pteridophytes. The simplest form of the gametophyte among the Hepaticse is found in the thallose Jungermanniacese and Anthocerotes. In such forms as Aneura (Fig. 38) and Anthoceros (Fig. 55) the thallus is made up of almost perfectly uniform chlorophyll- bearing tissue, fastened to the earth by means of simple rhizoids. In forms a little more advanced, e. g., Metzgeria, Pallavicinia (Fig. 38), there is a definite midrib present. From this stage there has been a divergence in two directions. In one series, the Marchantiacese, there has been a specialisa- tion of the tissues, with a retention of the thallose form of the plant. In Riccia (Figs. 1-9) we find two clearly marked regions, a dorsal green tissue, with numerous air-spaces, and a ventral compact colourless tissue. In the higher Marchantia- cese (Fig. 16) this is carried still further, knd the air-chambers often assume a definite form, and a distinct epidermis with characteristic pores is formed. In the Marchantiacese also ventral scales or leaf-like lamellse are developed, and rhizoids of two kinds are present. Starting again from the flat, simple thallus of Anciira there has been developed the leafy axis of the more specialised Jungermanniacese. Between the latter and the strictly thallose forms are a number of interesting inter- mediate forms, like Blasia and Fossornhronia, where the first indication of the two dorsal rows of leaves is met with ; and in • Blasia at least the rudiments of the ventral row of small leaves (amphigastra) usually found in the foliose forms are present. The tissues of the Liverworts are very simple, and consist for the most part of but slightly modified parenchyma. Occa- sionally (Preissia) thickened sclerenchyma-like fibres occur, II MUSCINE^—HEPA TICJE— MARCH ANT I ALES 1$ but these are not common. Mucilage cells of various kinds are common. The secreting cells may be hairs on the ventral surface, and especially developed near the apex, where the mucilaginous secretion serves to protect against drying up ; or they may be isolated (Marchautia) or rows of cells (Cono- cephahis) within the tissue of the thallus. The growth of the gametophyte is usually due to the division of a single apical cell. In some of the thallose forms, e.g., Marchantiaceas, Anthocerotes, a single initial cell is not always to be recognised in the older thallus, but in these forms a single initial always appears to be present in the earlier stages. In the Jungermanniacese, howxver, a single apical cell is always distinguishable, but varies a good deal in form in different genera, at least among the thallose forms, or even in the same genus. Among the foliose Jungermanniacese it always has the form of a three-sided pyramid. From the apical cell seg- ments are cut off in regular succession, and the first divisions of the segments also show much regularity, and often bear a definite relation to the tissues of the older parts. The Sexual Organs The archegonium is always traceable to a single cell, but the position of the mother cell is very different in different genera. In the simplest cases, e.g., Riccia, Sphcerocarpns (Figs. 2, 29), the mother cell is formed from a superficial cell of one of the youngest dorsal segments of the apical cell, close to the growing point of an ordinary branch of the thallus, whose growth is in no way affected by the formation of arche- gonia. In such forms the archegonia stand alone, and about each is developed a sort of involucre by the growth of a ring of cells immediately surrounding the archegonium rudiment. In other cases the archegonia are found in groups, e. g., Palla- vicinia (Fig. 38), separated by spaces where no archegonia are found. Here each group of archegonia has a common invol- ucre. In Aneiira and most of the higher Marchantiacese the archegonia are found in the same way, but upon special modi- fied branches. In the foliose Jungermanniaceae the origin of the archegonia is somew^hat different. Here they are formed upon short branches, where, after a small number of perichsetial leaves have been formed, the subsequent segments of the apical i6 MOSSES AND FERNS chap. cell develop archegonia at once, and finally the apical cell itself becomes the mother cell of the last-formed archegonium, and, of course, with this the growth in length of the branch ceases. With the exception of the Anthocerotes, where the arche- gonium mother cell does not project at all, it quickly assumes a papillate form and is divided by a transverse wall into a basal cell, and an outer one from which the archegonium itself develops. The divisions in this outer cell are remarkably uniform. Three vertical walls are first formed, intersecting so as to enclose a central cell (Fig. 2, G). In this central cell a transverse wall next cuts off a small, upper cell (cover cell) from a lower one. Subsequently the three (or in the Jungermanniacese usually but two) first- formed peripheral cells divide again vertically, and by transverse walls in all of the peripheral cells, and somewhat later in the central one also, the young archegonium is divided into two tiers, a lower one or venter, and an upper one, the neck (Fig. 2, F). The middle cell of the axial row, by a series of transverse walls, gives rise to the row of neck canal cells, and the lowermost cell divides into two an upper one, the ventral canal cell, and a larger lower one, the egg. The antheridium shows very much greater diversity in its structure, and equally great difference in its position. The origin in the thallose forms is usually the same as that of the archegonium, and indeed where the two grow mixed together, as in many species of Riccia, it is sometimes difficult to distinguish them in their earliest stages. Usually, however, the antheridia are borne together, either on special branches {Marchantia, species of Aneura), or they are produced in a special part of the ordinary thallus, which usually presents a papillate appearance (e.g., Fimhriaria) . In the foliose Junger- manniacese the antheridia are often borne singly in the axils of slightly modified leaves, but in no case does the apical cell of the shoot become transformed into an antheridium. The antheridium, like the archegonium, arises from a single super- ficial cell. The first division usually divides the primary cell into a stalk cell and the body of the antheridium. The first may remain very short and undergo but few divisions, or it may develop into a stalk of considerable length. The first division in the upper cell may be either transverse (Marchan- tiacese, Sphcorocarpus) or vertical (Jungermanniacese). II MUSCINEJE—HEPA TIC^— MARCH ANTI ALES 17 Later, by a series of periclinal walls, a central group of cells is separated from an outer single layer of cells. The latter divide only a few times, and develop chlorophyll, which sometimes changes into a red or yellow pigment at maturity. The inner cells give rise to a very large number of sperm cells, which in most Hepatic?e are extremely small, and consequently not well adapted to studying the development of the spermatozoids. In a few forms, however, they are larger ; and in Pellia especially, where the sperm cells are relatively large, the development has been carefully studied by Guignard (i), Buchtien (i), and others of late years, as well as by many of the earlier observers, and a comparison with other Hepaticse shows great uniformity in regard to the origin and development of the spermatozoid. After the last division of the central cells the nuclei retain their flattened form, and thus the sperm cells or spermatids remain in pairs, an appearance very common in the ripe antheridium of most Liverw^orts. Just before the differentiation of the body of the spermatozoid begins, the nucleus has the appearance of an ordinary resting nucleus, but no nucleolus can be seen. The first change is an indentation in the edge of the discoid nucleus, and this deepens rapidly until the nucleus assumes a crescent form. One of the ends is somewhat sharper and more slender than the other, and this constitutes the anterior end. As the body of the spermatozoid grows in length it becomes more and more homogeneous, the separate chromosomes apparently fusing together as the body develops. The body of the spermatozoid increases in length until it forms a slender spiral band coiled in a single plane, lying parallel with the one in its sister cell. The full-grown spermatozoid in Pellia epiphylla has, according to Guignard ((i), p. 67) from three to four complete coils. Usually when the spermatozoid escapes, it has attached to the coil a small vesicle which swells up more or less by the absorption of water. This vesicle is the remains of the cytoplasm of the cell, and may, perhaps, contain also some of the central part of the nucleus. Gui- gnard ((i), p. 66) asserts that sometimes the cytoplasm is all used up during the growth of the spermatozoid, and that the free spermatozoid shows no trace of a vesicle. In the Ricciacese and in Spliccrocarpus new archegonia continue to form even after several have been fertilised, so that numerous sporogonia develop upon the same branch of the 2 i8 MOSSES AND FERNS chap. thallus; but in most Liverworts the fertilisation of an arche- gonium checks the further formation of archegonia in the same group, and only those that are near maturity at the time reach their full development ; and even if more than one archegonium of a group is fecundated, as a rule but one embryo comes to maturity. The Sporophyte Unquestionably the lowest type of sporogonium is found in Riccia (Fig. 6). Here the result of the first divisions in the embryo is a globular mass of cells, which a little later shows a single layer of peripheral cells and a central mass of spore mother cells, all of which produce spores in the usual way. The sporogonium remains covered by the venter of the arche- gonium until the spores are ripe, and never projects above the surface of the thallus. The spores only escape after the thallus (or at least that part of it containing the sporogonia) dies and sets them free as it decays. In the genus Sphcerocarpus (Fig. 30), which may be taken to represent the next stage of develop- ment, we notice tw^o points in which it differs from Riccia. In the first place there is a basal portion (foot), which is simply an absorbent organ, and takes no part in the production of spores. Secondly, only a part of the archesporium develops perfect spores. A number of the spore mother cells remain undivided, and serve simply to nourish the growing spores. In the majority of the Hepaticge the sporogonium shows, besides the foot and the capsule, an intermediate portion, the stalk or seta, which remains short until the spores are ripe, when, by a rapid elongation of its cells, the capsule is forced through the calyptra and the spores are discharged outside. In these forms, too, some of the cells of the archesporium remain undivided, and very early are distinguished by their elongated shape from the young spore mother cells. These elongated cells later develop upon the inner surface of the cell wall peculiar spiral thickened bands, which are strongly hygroscopic. These peculiar fusi- form cells, the elaters, are found more or less developed in all the Hepaticse except the lowest ones. The dehiscence of the sporogonium is different in the different orders. In the Ricciacese and some Marchantiacese the ripe sporogonium opens irregularly; in a few cases (species of Fimbriaria) the top of the capsule comes off as a lid; ir II MUSCINE^—HEPA TICJE— MARCH ANT I ALES 19 most Jungermanniales the wall of the capsule splits vertically into four valves. The spores are always of the tetrahedral type, i.e., the nucleus of the spore mother cell divides twice before there is any division of the cytoplasm, although this division may be indicated by ridges projecting into the cell cavity, and partially dividing it before any nuclear division takes place. The four nuclei are arranged at equal distances from each other near the periphery of the mother cell, and then between them are formed simultaneously cell walls dividing the globular mother cell into four equal cells having a nearly tetrahedral form. These tetrads of spores remain together until nearly full grown, or in a few cases until they are quite ripe. In the ripe spore two, sometimes three, distinct coats can be seen, the inner one (endospore, intine) of unchanged cellulose, the outer one (exospore, exine), strongly cutinized and usually having upon the outside characteristic thickenings, ridges, folds, spines, etc. Where these thickenings are formed from the outside they constitute the third coat (perinium, epispore). The exospore is especially well developed in species where the spores are exposed to great heat or dryness, and which do not germinate at once. In those species that are found in cooler and moister situations, especially where the spores germinate at once, the exospore is frequently thin. The nucleus of the ripe spore is usually small. The cytoplasm is filled with granules, mostly albuminous in nature, with some starch and generally a great deal of fatty oil that renders the contents of the fresh spore very turbid. Some forms, especially the foliose Junger- manniacese, have also numerous chloroplasts, but these are lack- ing usually in those forms that require a period of rest before germination. In Pellia and Conocephahis the first divisions in the germinating spore take place while the spores are still within the sporogonium. The germination of the spores begins usually by the forma- tion of a long tube (germ-tube, "Keimschlauch" of German authors), into which pass the granular contents of the spore. At the same time there may be formed a rhizoid growing in a direction opposite to that of the germinal tube, although quite as often the formation of the first rhizoid does not take place until a later period. If the spore does not contain chlorophyll before germination, it is developed at an early stage, before any 20 • . MOSSES AND FERNS chap. cell-divisions occur. Often the formation of a germ-tube is suppressed and a cell surface or cell mass is formed at once, and all these forms may occur in the same species. The germination only takes place when the light is of sufficient intensity, and the amount of light is a very important factor in determining the form of the young plant. Thus if the light is deficient, the germ-tube becomes excessively long and slender, and divisions may be entirely suppressed. An excess of light tends to the development at once of a cell surface or cell mass. In the simpler thallose forms the first few divisions in the young plant establish the apical cell, and we cannot properly speak of the gametophore as arising secondarily from a protonema ; in other cases, however, the young plant does arise as an outgrowth or bud from a protonema, which only rarely has the branching filamentous character of the Moss protonema. Classification of the Hepaticae The Hepaticae are readily separated into the two following well-marked orders : Order I Marchantiales. Order II. Jungermanniales. The following diagnoses are taken, with some modifica- tions from SchifTner ((i), p. 5) : Order I. Marchantiales. Gametophyte always strictly thallose, composed of several distinct layers of tissue, the uppermost or chlorophyll-bearing cells usually containing large air-spaces. The dorsal epidermis usually provided with pores, ventral surface with scales ar- ranged in one or two longitudinal rows. Rhizoids of two kinds, those with smooth walls, and papillate ones; sexual organs, except in the lowest forms, united in groups which are often borne on special stalked receptacles. The first divisions of the embryo are arranged like the quadrants of a sphere. Sporogonium either with or without a stalk, and all the inner cells forming spores, or some of them producing elaters. No columella present. II MUSCINEyE—HEPA TIC^— MARCH ANTI ALES 21 Fam. I. Ricciacccc Chlorophyll-bearing tissue with or without air-chambers, and, where these are present, they never contain a special assim- ilative tissue. Epidermal pores wanting or rudimentary. Sexual organs immersed in open cavities upon the dorsal surface. Sporogonium without foot or stalk, and remaining permanently within the venter of the archegonium. All the cells of the archesporium produce spores. Fam. 2. Corsiniacece. Air-chambers well developed; epidermis with distinct pores; sexual organs in distinct groups, but the receptacles always sessile ; sporogonium with a short stalk, producing besides the spores sterile cells, which may have the form of very simple elaters. Fam. 3. MarchantiacecB. Air-chambers usually highly developed, and the chambers often containing a loose filamentous assimilative tissue. Pores upon the dorsal surface always present (except in Diimortiera and Monoclea) and highly developed, ring-shaped or cylin- drical. Sexual organs always in groups, usually upon special long-stalked receptacles. Sporophyte stalked and when ripe breaking through the calyptra, opening by teeth or a circular cleft, more seldom by four or eight valves. The archesporium develops sterile cells, in the form of elaters, as w^ell as spores. The Marchantiales constitute a very natural order of plants, all of whose members agree very closely in their funda- mental structure. The separation of the Ricciacese as a group co-ordinate with the Jungermanniales and Marchantiales is not warranted, as more recent investigations, especially those of Leitgeb ( (7), vol. iv.) have shown that the two groups of the Marchantiacese and Ricciacese merge almost insensibly into each other. They are all of them strictly thallose forms, the thallus being unusually thick and fleshy, and range in size from a few millimetres in some of the smaller species of Riccia, to 10 to 20 centimetres in some of the larger species of Diimortiera and Conocephahis. In most of them branching is prevailingly 22 MOSSES AND FERNS CHAP. dichotomous, and as this is rapidly repeated, it often causes the thallus to assume an orbicular outline. Some forms, however, 1 Fig. I. — Marchantiales. A, B, Male plants of Fimbriaria Californica. A, from above; B, from below; (^, antheridial receptacle; /, ventral lamellae, X4; C, Riccia glauca, X6; sp, sporogonia; D, Conocephalus conicus, X4; E, Targionia hypophylla, X2; ^, antheridial branch. e.g., Targionia (Fig. i, E), may fork comparatively seldom, and the new branches are for the most part lateral. The thallus II MUSCINE^—HEPA TIC^— MARCH ANTI ALES 23 is fastened to the substratum by rhizoids, which are unicellular and usually of two kinds, those with smooth walls and those with peculiar papillate thickenings or teeth that project inward (Fig. 12). The cells of the lower layers of tissue are usually nearly or quite destitute of chloroplasts, which, however, occur in large numbers in the so-called chlorophyll-bearing layer, just below the dorsal epidermis. This chlorophyll-bearing layer contains air-spaces in all forms except some species of Dumortiera and M on odea, and these spaces are either simple narrow canals, as in Riccia glmica, or they may be large cham^ bers separated by a single layer of cells from their neighbors. Such forms occur in most of the higher Marchantiaceae. The grow^th of the thallus is due to the division of a small group of cells occupying the bottom of the heart-shaped indent- ation in the forward part of the thallus. Sections parallel to the surface, cutting through this group, show a row of mar- ginal cells that appear very much alike, and it is impossible always to tell certainly whether or not there is a single definite initial cell. Such a single initial is unquestionably present in the earlier stages, and it is quite possible that it may persist, but owing to its small size and its close resemblance to the adjoin- ing cells, this cannot be positively asserted. In vertical sections the initial cell (or cells) appears nearly triangular, with the free outer wall somewhat convex. From this cell two sets of segments are cut off, the dorsal segments giving rise to the green tissue, and the lower segments producing the ventral lamellae and colourless lower layers of cells of the thallus. The plants multiply asexually either by the older parts of the thallus dying away and leaving the growing points isolated, or lateral branches, which are often produced in great numbers from the lower surface of the midrib, become detached and each branch forms a separate plant. The wxll-known gemmae of Marchantia and Lunularia are the most striking examples of special asexual reproductive bodies. The sexual organs are always derived from the dorsal segments of the apical cell, either of the ordinary branches or of special shoots. The archegonium is of the typical form, and the antheridium always shows a series of transverse divisions before any longitudinal walls are formed in it. While the gametophyte may reach a very considerable degree of specialisation, the sporophyte is relatively insignifi- 24 MOSSES AND FERNS chap. cant even in the higher forms, and has the foot and stalk poorly developed. While the Marchantiales grow for the most part in moist situations, and some of them, e.g., Marchantia poly- morpha, are very quickly killed by drying, some species, e.g., Riccia trichocarpa, a common California species, grow by pref- erence in exposed rocky places exposed to the full force of the sun. This latter species as well as several others of the same region, e.g., Fimbriaria Calif ornica, Targionia hypophylla, do not die at the end of the rainy season, but become completely dried up, in which condition they remain dormant until the autumn rains begin, when they absorb water and begin to grow again at once. In these cases usually only the ends of the branches remain alive, so that each growing tip becomes the beginning of a new plant. The Ricciace^ As a type of the simplest of the Marchantiacese, we may take the genus Riccia, represented, according to Schiffner ((i), p. 14), by 107 species, distributed over the whole earth. Most of them are small terrestrial plants forming rosettes upon clay soil or sometimes in drier and more exposed places. A few species, e.g., R. Huitans, are in their sterile condition sub- mersed aquatics, but only fruit when by the evaporation of the water they come in contact with the mud at the bottom. The dichotomously branched thallus shows a thickened midrib, which is traversed upon the dorsal surface by a longi- tudinal furrow which in front becomes very deep. At the bottom of this furrow, at the apex of the thallus, lies the grow- ing point. A vertical section through this shows a nearly triangular apical cell which lies much nearer the ventral than the dorsal surface (Fig. 2, x). From this are cut off succes- sively dorsal and ventral segments. Each segment next divides into an inner and an outer cell. From the outer cells of the dorsal segments the sexual organs arise, and from those of the ventral segments the overlapping lamellae upon the lower surface of the thallus, and also the rhizoids. The rapid division of the inner cells of the segments, especially those of the dorsal ones, causes the thallus to become rapidly thicker back of the apex. Sections made parallel to the surface of the thallus, and passing through the growing point (Fig. 3), show II MUSCINEAL— HEPATIC^— MARCH ANTI ALES 25 that the margin is occupied by a group of cells that look very much alike. Sometimes one of these cells is somewhat larger than the others, but more commonly it is impossible to decide with certainty that a single initial is present. From a com- parison of the two sections it is at once evident that the initial cells have nearly the form of the segment of a disc, and that in addition to the dorsal and ventral segments lateral ones are cut off as well. In the region just back of the apex the tissue of Fig. 2. — Riccia glauca. Development of the archegonium, XS^S- A, Vertical section through the growing point; x, apical cell; ar, young archegonium; //, ventral lamellae; B-F, successive stages in the development of the archegonium, seen in longitudinal section; G, cross-section of young archegonium (diagrammatic). the thallus is compact, but in the older parts a modification is observable both on the dorsal and ventral surfaces. In the former, a short distance from the growling point, the superficial cells project in a papillate manner above the surface. This causes little depressions or pits to be formed between the adja- cent cells (Fig. 3, C). The subsequent divisions in the papillae are all transverse, and this transforms each papillate surface cell into a row of cells which, as it elongates, causes the pits between it and the adjacent ones to become deep but narrow air-channels, so that in the older parts of the thallus the upper portion is composed of closely-set vertical rows of chlorophyll- bearing cells separated by narrow clefts opening at the surface. 26 MOSSES AND FERNS CHAP. In Riccia glauca, as well as other species, the uppermost cell of each row often enlarges very much, and with its fellows in the other rows constitutes the epidermis. According to Leitgeb's researches this epidermal cell is formed by the first division in the outer cell of the segment, and either undergoes no further division, or by dividing once by a transverse wall forms a two- layered epidermis ( R. BischoMi). On the ventral side the outer cells of the segments project in much the same way, but Fig. 3. — Riccia glauca. Horizontal sections of the growing point. A, B, X525; C, X about 260. C shows the dichotomy of the growing point; x, x' , the two new growing points; L, the lobe between them; ar, a young archegonium. they remain in close contact laterally with the neighboring cells, so that instead of forming isolated rows of cells, transverse plates or lamellae, occupying the median part of the lower sur- face of the thallus, are formed. These remain but one cell thick, and grow very rapidly, and bend up so as to completely protect the growing point. With the rapid widening of the thallus in the older parts these scales are torn asunder, and the two halves being forced apart constitute the two rows of ventral scales found in the older parts. Later these scales dry up and It MUSCINEM—HEPA TIC^—MARCHANTIALBS 27 are. often scarcely to be detected except close to the growing point. In the case of Ricciocarpiis natans (Leitgeb (7), iv., p. 29) instead of a single scale being formed, each cell of the horizon- tal row, which ordinarily gives rise to a single scale, grows out independently, much as do the dorsal surface cells in the other species, and the result is a horizontal series of narrow scales, each one corresponding to a single cell of the original row. These later are displaced by the subsequent growth of the thallus, and their arrangement in transverse series can only be seen in the younger parts. The very rapid increase in length of the dorsal rows of cells as they recede from the growing point soon causes them to overarch the latter, which thus comes to lie in a deep groove ; indeed not infrequently the end cells of the rows on opposite sides of the groove actually meet, so that the groove becomes a closed tube. R. Unitans (Leitgeb (7), iv. p. 11) and R. crysfaUina differ in some respects from the other forms. In these, owing to a greater expansion of the tissues of the older parts of the thallus, the air-spaces are very much enlarged. In the former they are almost completely closed above, as the epidermal cells, by repeated vertical divisions, keep pace with the growth of the thallus and form a continuous epidermis, wath only a small central pore over each of the large air-chambers. In R. crys- tallina, however, there is no such secondary growth of the epidermal cells, and in consequence the cavities are completely open above, so that the surface of the thallus presents a series of wide depressions separated by thin lamellae. These tw^o species also show some difference as to the ventral scales. Those of R. Unitans are small and do not become separated into two, and in R. crystallina they are wanting entirely. Most of the Ricciacese multiply by special adventive shoots that arise from the ventral surface of the midrib. These become detached and form new individuals. According to Fellner ( i ) the rhizoids develop at the apex a young plant in a manner entirely similar to that by which the young plant arises from the germ tube of the germinating spore. By far the commonest method of branching in most species of Riccia is a true dichotomy. The first indication of this process is a widening of the growing point and a correspond- 28 MOSSES AND FERNS chap. ing increase in the number of the marginal cells. The central cells of the marginal group now begin to grow more vigorously than the others and to project as a sort of lobe (Fig. 3, C, L), and this lobe divides the initial cells into two groups lying on either side of it. As soon as this is accomplished each new group of initial cells continues to grow in the same manner as the original group, and two new growing points are estab- lished, each of which develops a separate branch. The growth of the middle lobe is limited, and it remains sunk in the fork between the two new branches. The thallus is attached to the substratum by rhizoids of two kinds. The first are smooth-walled elongated cells, with colourless contents, the others much like those of the higher Marchantiacese. Their walls are undulating, and projecting inward are numerous more or less developed spike-like protu- berances. The rhizoids arise from large superficial cells of the ventral part of the midrib. They are readily distinguished from the adjacent cells by their much denser contents, even before they have begun to project. The arrangement of the tissues of the fully-developed thallus is best seen in vertical cross-sections. In R. glauca and allied forms four well-marked tissue zones can be readily recognized in such a section. The lowest consists of a few layers of colourless rather loose parenchyma, from which the rhizoids arise, and to which the ventral lamellae are attached. Above this a more compact, but not very clearly limited region, the midrib. The elongated form of the midrib cells, which contain abundant starch but no chlorophyll, is, of course, not evident in cross-section. Radiating from the midrib are closely-set rows of chlorophyll-bearing cells with the charac- teristic narrow air-spaces between. The median furrow is very conspicuous in such a section, and extends for about half the depth of the thallus. Terminating each row of green cells is the enlarged colourless epidermal cells, often extended into a beak-like appendage. In some species, e.g., R. trichocarpa, some of the surface cells grow out into stout thick-walled pointed hairs. The Sexual Organs In Riccia the sexual organs are formed in acropetal suc- cession from the younger segments of the initial cells, and II MUSCINE^—HEPA TIC^— MARCH ANTI ALES 29 continue to form for a long time, so that all stages may be met with upon the same thallus. While both antheridia and arche- gonia may be found together, in the two species R. glauca and R. trichocarpa, mainly studied by myself, I found that as a rule several of one sort or the other would be formed in succession, and that not infrequently antheridia were quite wanting upon plants that had borne numerous archegonia. Both archegonia and antheridia arise from single superficial cells of the younger dorsal segments of the initial cells. In their earliest stages they are much alike, the mother cell of the antheridium being, however, usually somewhat larger than that of the arche- gonium. The cell enlarges and projects as a papilla above the surface, when it is divided by a transverse wall into an outer cell and an inner one. The latter divides but a few times and forms the short stalk ; the outer cell, which has dense granular contents, develops into the archegonium or antheridium as the case may be. In the former case the divisions follow the order already indicated for the typical Liverwort archegonium. In the outer cell, which continues to enlarge rapidly, a nearly vertical wall is formed (Fig. 2, C), which divides the cell into two very unequal parts. This wall is curved and strikes the periphery of the mother cell at about opposite points (Fig. 2, G, i). A second wall of similar form is next formed in the larger cell (G, 2), one end of which intersects the first wall, and finally a third wall (3) intersecting both of the others is formed. The young archegonium seen in vertical section at this stage (Fig. 2, D) shows a large central cell bounded by two smaller lateral ones ; in cross-section the central one appears triangular. Each of the four cells of which the arche- gonium rudiment is now composed divides into two. The outer ones each divide by radial walls into equal parts, and the central one divides into an upper smaller cell (cover cell) and a lower larger one (Fig. 3, E). The next divisions are hori- zontal and divide the young archegonium into two tiers of cells. The lower one forms the venter, and the upper one the neck, and next the cover cell divides into four nearly equal cells by intersecting vertical walls. The archegonium at this stage (Fig. 2, F) is somewhat pear-shaped, being smaller at the bottom than at the top, and the basal cell is still undivided. It now rapidly increases in length by the transverse division and growth of all its cells, and there is at the same time a 30 MOSSES AND FERNS CHAP. marked increase in diameter in the venter, which finally becomes almost globular (Fig. 4). The axial cell of the neck, the neck canal cell, divides, according to Janczewski (i), always into four in R. BischofHi, and the same seems to be true for R. fricho- carpa (Fig. 4, A), and probably is the same in other species. The number of divisions in the outer neck cells is various, but is most active in the lower part, but in the central cell of the venter there is always but a single transverse division which Fig. 4. — ^A, Archegonium of Riccia trichocarpa, showing the ventral canal cell (f), XS25; B, ripe archegonium of R. glauca, longitudinal section, X260. separates the ventral canal cell from the ^gg. The four primary cover cells enlarge a good deal as the archegonium approaches maturity, and divide by radial walls usually once, so that the complete number is normally eight — Janczewski gives ten in R. BischoMi. The basal cell finally divides into a single lower cell which remains undivided, completely sunk in the thallus, and an upper cell which divides into a single layer of cells forming part of the venter, and continuous with the other peripheral cells. The mature archegonium (Fig. 4) n MUSCINE^— HEPATIC^— MARCHANTIALES 31 has the form of a long-necked flask with a much enlarged base. The canal cells are completely indistinguishable, their walls having become absorbed and the contents run together into a granular mass. The nuclei of the neck-canal cells are small and not readily recognisable after the breaking down of the cell walls, but from analogy with the higher forms it is not likely that they completely disappear in the ripe archegonium. The cytoplasm of the central cell contracts to form the naked globular Qgg. The cytoplasm is filled with granules, and the nucleus, which is of moderate size, shows a distinct nucleolus, but very little chromatin. A special receptive spot was not certainly to be seen. Almost coincident with the first cell division in the arche- gonium rudiment there is a rapid growth of the cells imme- diately surrounding it. These grow up as a sort of ring or ridge about the archegonium, which is thus gradually immersed in a cup-shaped cavity, and the growth of the cells about this keeps pace with the increase in length of the archegonium, so that even when fully grown only the very extremity of the neck projects above the level of the thallus. The whole process is undoubtedly but a modification of the ordinary growth of the dorsal part of the thallus, and the space about the arche- gonium is the direct equivalent of the ordinary air-spaces. The first division in the primary antheridial cell is the same as in the archegonium, but the later divisions differ much and do not show such absolute uniformity. The first division wall in the upper cell (Fig. 5, B) is always transverse, and this is followed by a second similar wall, but the subsequent divisions show considerable variation even in the same species. After a varying number of transverse walls have been formed, in most cases the next divisions, which are formed only in the middle segments, are vertical, and divide the segments into quadrants of a circle when seen in transverse section. Occa- sionally a case is met with where the division walls are inclined alternately right and left, and the divisions strongly recall those of the typical Moss antheridium (Fig. 5, D). The separation of the sperm cells is brought about by a series of periclinal walls in a number of the middle segments, by which four central cells in each segment (Fig. 5, G) are separated from as many peripheral cells. These central cells 22 MOSSES AND FERNS CHAP. have, as usual in such cases, decidedly denser contents than the peripheral ones. The lower one or two segments and the terminal ones do not take part in the formation of sperm cells, but simply form c A. Ql (!) Fig. s. — A-F, Development of the antheridium of R. glauca, seen in longitudinal section; G, cross-section of a young antheridium of the same; H, antheridium of R. trichocarpa; I, sperm cells of R. glauca. Figs. E, F, X150; I, X600, the others X300. part of the wall of the antheridium. The central cells now divide with great rapidity, the division walls being formed nearly at right angles to each other, so that the central part of the antheridium becomes filled with a very large number of nearly cubical cells. The divisions are formed with such regularity that the boundaries of the original central cells remain very clearly marked until the antheridium is nearly mature. The basal cell of the antheridium rudiment in R. glauca divides once by a horizontal wall (Fig. 5, B, D) and forms the short stalk of the antheridium, which, however, is almost completely sunk in the thallus. Between this stalk and the central group of cells there are usually two layers of cells, so that the wall of the antheridium is double at the base, while it has but a single layer of cells in the other parts. The II MUSCINEM— HEPATIC^— MARCH ANTI ALES 33 uppermost cells are often, althoug-h not always, extended into a beak. The spermatozoids do not seem to differ either in their method of development or structure from those of other Hepatic?e, but their excessively small size makes it extremely difficult to follow through the details of their development. When ripe the wall cells are much compressed, but are always to be distinguished. Like the archegonia, the antheridia are sunk separately in deep cavities, which are formed in exactly the same way. Unlike the archegonia, however, the antheridium does not nearly reach to the top of the cavity, whose upper walls are in many species very much extended into a tubular neck, which projects above the general level of the thallus, and through which the spermatozoids are discharged. The Sporophyte. After fertilisation is effected the tgg develops at once a cell-membrane and enlarges until it completely fills the cavity of the venter. The first division w^all is more or less inclined to the axis of the archegonium, but approaches usually the horizontal. The lower of the tw^o cells thus formed divides first by a wall at right angles to the first formed, but this is followed in the upper half of the embryo by a similar division, so that the embryo is divided into nearly equal quadrants. In each of the quadrants a wall meeting both of the others at right angles next appears (Fig. 6, C, III), and the embryo at this stage consists of eight nearly equal cells. The next walls are not exactly alike, but the commonest form is a curved wall (Fig. 6, C), striking two of the others, usually walls II and III, and intersecting the surface of the embryo. This wall divides the octants into two cells, which appear respectively triangular and quadrilateral in section. By the next division the arche- sporium is separated from the wall of the sporogonium. These W2.\\s, are periclinal, and by them a single layer of outer cells is separated from the central mass of cells which constitutes the archesporium (Fig. 6, B, D). At first the cells of the embryo are much alike, but as it grows the inner cells increase in size and their contents become densely granular, while the outer cells grow only in breadth, and not at all in depth, assuming more and more a tabular 3 34 MOSSES AND FERNS CHAP. form, and for the most part undergo divisions only in a radial direction so that the walls remain but one cell thick in most places. As the sporogonium increases in diameter the central cells begin to separate and round off. Their walls become partially mucilaginous, and in microtome sections stain strongly with Bismarck-brown or other reagents that stain mucilaginous membranes. With this disintegration of the division walls the cells separate more and more until they lie free within the cavity of the sporogonium. Each of these spore mother cells is a large globular cell with thin membrane m. Fig. 6. — ^A, B, Young embryos of R. glauca in longitudinal section, showing the venter of the archegonium, X260; C, transverse section of a similar embryo, X260; D, longitudinal section of the archegonium and enclosed embryo of R. trichocarpa at a later stage, X220; m, the sterile cells of the sporogonium. and densely granular contents. The nucleus is not so large as is usually the case in cells of similar character, and, except the nucleolus, stains but slightly with the ordinary nuclear stains. In the fresh state these spore mother cells are absolutely opaque, owing to the great amount of granular matter, largely drops of oil, that they contain. In embedding these in paraffine, however, the oil is dissolved and removed, and microtome sections show the fine granules of the cytoplasm arranged in a net-like pattern, the spaces between probably being occupied by oil in the living cells. II MUSCINE^— HEPATIC^— MARCH ANTI ALES 35 Fig. 7, A shows the nucleus of the mother cell under- going the first division. The small size of the nuclei, and the small amount of chromation in them, make the study of the details of the nuclear division difficult here, and as there was nothing to indicate any special peculiarities these were not followed out. After the first nuclear division the daughter nuclei divide again, after which the four nuclei arrange them- c. Fig. 7.—Riccia trichocarpa. A, Section of a spore mother cell undergoing its first division, X6oo; B, section of young spore tetrad, X300; C, section of ripe spore, X300; D, surface view of the exospore of a similar stage, X300. selves at equal distances from each other, the division w^alls form simultaneously between them, dividing the spore mother cell into the four tetrahedral spores. A section through such a young spore-tetrad is shown in Fig. 7, B, where one of the cells is somewhat shrunken in the processof embedding. The cell walls at this stage are very delicate and of unchanged cellulose ; but as they grow older the wall soon shows a separa- tion into endospore and exospore. The latter in R. tricho- carpa, which was especially studied, is very thick, at first yellowish in colour, but deepening until when ripe it is black. Sections parallel to the surface show in this species what appear to be regular rounded pits, but vertical sections of the spore-coat show that this appearance is due to a peculiar fold- 36 MOSSES AND FERNS chap. ing of the exospore, which also shows a distinct striation, the outer layer being much thicker and denser than the inner ones. The nucleus of the ripe spore is remarkably small, and it is evident that the dense contents of the ripe spore are largely oil or some similar soluble substance, as in microtome sections there is very little granular matter visible. At the same time that the first division wall forms in the embryo, the outer cells of the venter begin to divide by periclinal walls, so that the single layer of cells in the wall of the unfertilised archegonium becomes changed into two, and the basal portion becomes still thicker; the neck takes no part in this later growth. The cells of the venter develop a great deal of chlorophyll, which is quite absent from the sporogonium itself, and before the spores are ripe the inner layer of cells of the calyptra (venter) becomes almost entirely absorbed, so that only traces of these cells are visible when the spores are ripe. The wall of the sporogonium also disappears almost completely as the latter matures, but usually in microtom.e sections traces of this can be made out in the ripe capsule, although the cells are very much compressed and partially disorganised. The contents of these cells, as well as the inner calyptra cells, no doubt are used up to supply the growing spores with nourish- ment. Thus, when ripe, the spores practically lie free in the cavity surrounded only by the outer layer of calyptra cells. The neck of the archegonium persists and is made conspicuous by the dark brown colour of the inner walls of the cells. Hitherto the germination of the Ricciacese was only known in R. glauca ( Fellner ( i ) ) . The account here given is based upon observations made upon R. trichocarpa — a very common Californian species. It fruits in winter and early spring, and the spores remain dormant during the dry summer months. If the spores are sown in the autumn they germinate within a few days by bursting the massive black exospore, through which the colourless endospore enclosing the spore contents projects in the form of a blunt papilla. This rapidly grows out into a long club-shaped filament (Fig. 8, A), much less in diameter than the spore, and into this the spore contents pass. These now contain albuminous granules and great numbers of oil-globules, and some chlorophyll bodies, which at first are small and not very numerous. They, however, increase rapidly in size, and divide also, so that before the first cell division II MUSCINEAi— HEPATIC^— MARCH ANTI ALES 37 takes place the chloroplasts are abundant and conspicuous. The formation of the first rhizoid does not take place usually until a number of divisions have been formed in the young thallus. The first rhizoid (Fig. 9, r) arises at the base of the germinal tube, and is almost free from granular contents. It, usually at least, is separated by a septum from the germ-tube. The first wall in the latter is usually transverse, although in exceptional cases it is oblique (Fig 8, C), and this is followed by a second one parallel to the first (Fig. 8, C). In each of these cells a vertical wall is formed, and then a second at right angles to this, so that the nearly globular mass of cells at the Fig. 8. — Riccia trichocarpa. Germination of the spores, X190. In E the figure at the left represents a surface view, the one at the right an optical section; K, germinal tube. end of the germ-tube is composed of eight nearly equal cells or octants. As these divisions proceed the oil drops which are so abundant in the undivided germ-tube disappear almost com- pletely, and are doubtless used up by the growing cells. According to Leitgeb's view, and that of other authors, the eight-celled body at the end of the germ-tube is a sort of pro- tonema, from which the gametophore arises as a lateral out- growth. I have seen nothing in the species under consideration which supports such a view. Here the axis of growth is con- tinuous with that of the germ-tube, and in some cases at least, 38 MOSSES AND FERNS CHAP. and probably always, a single apical cell is developed at the apex at a very early stage. Probably this initial ^ell is one of the four terminal octant cells resulting from the first divisions. This cell sometimes has but two sets of segments cut off from it at first, alternately right and left, but whether this form is constant in the young plant I cannot now say. Fig. g.—Riccia trichocarpa. Later stages of germination. A, from below, X260; B, optical section of A, showing apical cell x, XS2o; C, X85; r, rhizoids. Inter- cellular spaces have begun to develop. The four lower quadrants also divide, at first only by transverse walls, and these cells lengthening give rise to a cylindrical body composed of four rows of cells, terminated by the more actively dividing group of cells at the summit. The single apical cell is soon replaced by the group of initials found in the full-grown gametophyte, and the method of growth from II MUSCINE^—HEPA TICAL— MARCH ANT I ALES 39 now on is essentially the same. The growth of the cells in the forward part of the dorsal surface of the young thallus is more active than that of the ventral side, so that they project over the growing point (Fig. 9), and as the outer cells of the lateral segments of the apical cell (or cells) also increase rapidly in size as they recede from the growing point, the forward margin of the thallus, seen from below, is deeply indented, and the forward part of the thallus is thus occupied by a deep cavity, at the bottom of which, toward the ventral side, lies the growing point. This cavity is the beginning of the groove or furrow found in the older thallus. At first the cells of the young thallus are without inter- cellular spaces, but at an early period (Fig. 9, C) the outer cells of the young segments separate and form the beginnings of the characteristic air-spaces. In R. trichocarpa some of the dorsal cells about the same time form short pointed papillae, the first indication of the pointed hairs characteristic of this species. As the plant grows, new rhizoids are formed by the growing out of ventral cells into papillae, which are cut ofif by a partition from the mother cell. These first-formed rhizoids are always smooth-walled, and it is only at a much later stage that the other form develops, as well as the ventral lamellae, which are quite absent from the young plant. Classification of the Ricciace^ Besides the genus Riccia, which includes all but three species of the family, there are two other genera, each represented by a single species, which undoubtedly belong here. Of these Ricciocarpus natans is of almost world-w^ide distribution. It is a floating form, like Riccia Huitans. Leitgeb ( (7), vol. iv.) has made a very careful study of the structure and development of the thallus, w^hich differs a good deal from that of Riccia, in which genus this plant was formerly placed. The apical growth is essentially the same, and the differentiation of the tissues begins in the same way, but the chlorophyll-bearing tissue is extraordinarily developed. The air-spaces are formed in the same way as in Riccia, but they become very deep, and at an early stage, while still very narrow, are divided by cel- lular diaphragms into several overlying chambers, which, nar- row at first, later become very wide, so that the dorsal part of 40 MOSSES AND FERNS CHAP. the thallus is composed of a series of large polyhedral air- chambers arranged in several layers, and separated by walls but one cell thick. The upper chambers communicate with the outside by pores, quite like those of the Marchantiaceae. The ventral tissue and midrib are rudimentary, and the very long pendent ventral lamellae are produced separately in trans- verse rows, which, however, become displaced by the later growth of the thallus, so that their original arrangement can no longer be made out. Oil bodies like those found in the Marchantiaceae occur. The terrestrial form, which grows on the margins of ponds, etc., where the floating form is found, is much more richly branched and more vigorous than the floating form (Fig. lo). The ventral scales become shorter, and numerous wide but unthick- ened rhizoids are formed, which are almost completely lacking in the floating form. The structure of the reproductive organs and sporogonium are essentially the same as in Riccia. Garber (i), who has recently studied the development of Riccio- carpus, finds that it is not dioecious, as has been frequently asserted, Fig. .o.-Ricciocarpus natans. A, but rather proteraudrous— that is, Floating form; B, terrestrial numcrous anther idia are formed, form, X2. ^^^ some time before the first arch- egonia develop. Occasionally no archegonia are formed. While the settling of the plant upon the mud is not a neces- sary condition for the development of the reproductive organs, as has been asserted by Leitgeb, still none are formed as a rule upon plants growing in permanent ponds, while those growing in temporary ponds regularly develop abundant reproductive organs. In permanent bodies of water, vegetative multipli- cation may be very rapid, and it has been found that after these are frozen over, a certain number of the plants survive, some- times sinking to the bottom, and resuming growth again in the spring. The third genus, Tesselina (Oxymifra), represented by the single species, T. pyramidata, is much less widely distributed, belonging mainly to Southern Europe, but also found in Para- 11 MUSCINEJE— HEPATIC JE— MARCH ANTI ALES 41 guay. This interesting form has also been carefully examined by Leitgeb ((7), iv., p. 34), who calls attention to its inter- mediate position between the RicciacCcC and the Marchantiaceae. The thallus has all the characters of the latter : air-chambers opening by regular pores, usually surrounded by six guard- cells ; two rows of ventral scales, independent from the begin- ning; and the sexual organs united into groups upon special parts of the thallus. The sporogonium, how^ever, is entirely like that of Riccia, so that it may properly be placed in the same family. The plants are dicecious and strictly terrestrial. A third genus, Croiiisia, represented also by a single species, C paradoxa, is placed provisionally with the RicciacCcC by Schififner ((i), p. 15), but the structure and development have not been investigated with sufficient completeness to make this certain. It has been found only in Brazil. Schiffner says of this form : "It belongs perhaps to the Corsinieae, and forms a direct transition from the Ricciacese to that family." The Corsiniace^ {Schiffner (i), p. 26). The family Corsiniaceae comprises but two genera, Corsinia and Funicitlaria (Boschia). Each genus contains but a single known species. Structurally they are intermediate in character between the Ricciaceae and Marchantiaceae. Corsinia differs from all the higher Marchantiaceae in the character of the ven- tral scales, which are formed in more than two rows, like those of Ricciocarpus. Boschia, the other genus, has two rows of scales of the ordinary form. The archegonia are borne in a group in a depression upon the dorsal surface of the thallus, but are not formed upon a special receptacle, although after fertili- sation the cells at the bottom of the cavity multiply actively and form a small prominence upon wdiich the young sporogonia are raised, and this may perhaps be the first indication of the arche- gonial receptacle in the other forms. The sporophyte resembles that of the Marchantiaceae, but the sterile cells in Corsinia do not develop into true elaters, and in both genera the foot is less developed than in the true Mar- chantiaceae. Marchantiace^. Comparing the Marchantiaceae wnth the Ricciaceae, the close similarity in the structure and development of the thallus is at 42 MOSSES AND FERNS chap. once apparent, but the former are more highly developed in all respects. The development of definite air-chambers in the green tissue, and a continuous epidermis with the characteristic pores, is common to all of them with the exception of the peculiar genera Dumorfiera and Monoclea, where the develop- ment of the air-chambers is partially or completely suppressed. The genera Ricciocarpiis and Tessalina on the one hand, and Corsinia and Boschia on the other, connect perfectly Riccia with the Marchantiacese as regards the structure of air-spaces and epidermis, as they do in other respects. The epidermal pores in the Marchantiacese are sometimes simple pores sur- rounded by more or less symmetrically arranged guard cells (Fig. 1 1, D), or they are, especially upon the female receptacles, of a most peculiar cylindrical form, which arises by a series of transverse walls in the primary guard cells (Fig. ii, C). There is a good deal of difference in the character of the air- chambers in different genera. In Rehoiilia and Fimhriaria, for instance, they resemble a good deal those of Ricciocarpiis, a more or less complete division of the primary chambers being produced by the formation of diaphragms or laminae, which give the green tissue an irregular honey-combed appearance, and in these forms there is not a sharp separation of the green tissue from the ventral colourless tissue. In other genera, Marchantia, Targionia (Fig. i8), Conocephalus, the dorsal part of the thallus is occupied by a single layer of very definite air-chambers, each opening at the surface by a single central pore. Seen from the surface the boundaries of these spaces form a definite network which in Conocephalus (Fig. i, D) is especially conspicuous. The bottom of these chambers is sharply defined by the colourless cells that lie below, and the space within the chamber is filled by a mass of short, branching, conferva-like filaments, which in the centre of the chamber have free terminal cells, but toward the sides are attached to the epidermal cells and are more or less confluent with the adjacent filaments. As in Riccia rhizoids of two kinds are present, but the thickenings to the tuberculate rhizoids (Fig. 12) are much more pronounced, and these are not infrequently branched, and may extend nearly across the cavity of the hair. The ventral scales are not produced by the splitting of a single lamella, as in Riccia, but are separate from the first and usually arranged II MUSCINE^— HEPATIC^— MARCH ANTI ALES 43 in two rows. Leitgeb ((7), iv., p. 17), recognises two types of these organs. In their earHest stages they are ahke, and both arise from papih^e close to the growing point. In both cases this papilla is cut off from a basal cell, but in the first type {Saiiteria, Targionia, Dumortiera) it remains terminal, usually forming the tip of a leaf-like terminal appendage of the scale. In the second type, represented by most of the other genera, this originally terminal papilla is forced to one side by the development of a lateral appendage to the scale, which, arising at first from a single cell, rapidly increases in A. CDSSI^ Fig. II. — Fimbriaria Californica. Development of the pores upon the archegonial receptacle, X260. A, B, C, in longitudinal section; D, view from above. size, and forms the overlapping dark purple marginal part of the scale so conspicuous in many species. In different parts of the thallus are found large mucilage cells, which are usually isolated ; or in Conocephalus, according to Goebel's (i) investigations, and those of Cavers (6), they may form rows of cells which become confluent so as to form mucilage ducts. In the earlier stages these cells have walls not differing from those of the adjacent cells, but as they grow older the whole cell wall is dissolved, and the space occupied by the row of young cells becomes an elongated cavity filled with apparently structureless mucilage. These cells are recog- nisable at an early period, as their contents are much denser and more finely granular than those of the adjacent cells. 44 MOSSES AND FERNS CHAP. ©c Small cells, each containing a peculiar oil body, are found abundantly in most species, both in the body of the thallus and in the ventral scales. The structure and development of these curious bodies, which are found also in many other Hepaticse, have been carefully studied by Pfeffer (2). The oil body has a round or oval form usually, and in the Mar- chantiese usually is found in a special cell which it nearly fills. It is brown or yellowish in colour, and has a turbid granular appearance. The extremely careful and exhaustive study of these bodies by Pfeffer has shown that the oil exists in the form of an emulsion in water, and that in addition to the oil and water more or less albuminous matter is pres- ent, and tannic acid. The latter is especially abundant in the oil bodies of Luniilaria, less so in Marchantia and Preissia ( Cavers ( 6) ; Kiister ( i ) ) . The thallus of the Marchantiacese is made up al- most entirely of parenchyma, but Goebel (3) states that in Preissia comniutata there are elon- gated sclerenchyma-like cells in the midrib. The walls of the large colourless cells of the lower lay- ers of the thallus are often marked with reticulate thickenings, which are especially conspicuous in Marchantia. Most of the Marchantiacese have no special non- sexual reproductive organs, but in the genera chantia poly- MaTchantia and Lunularia special gemmae are pro- mo r p /t a . (j^jced in enormous numbers; and in the latter tubercuiate form, w^hlch is extrcmcly common in greenhouses, rhizoid , ^j^g plant multiplies only by gemmae, as the plants are apparently all female. These gemmae, as is well known, are produced in special receptacles upon the dorsal side of the thallus. The receptacles are cup-shaped in Mar- chantia, and crescent-shaped in Lunularia, where the forward part of the margin of the cup is absent. These cups are appar- ently specially developed air-chambers, which, closed at first, except for the central pore, finally become completely open. The edge of the fully-developed receptacle is fringed. The gemmae arise from the bottom of the receptacle as papillate hairs, and their development is the same in the other two genera where they occur. Fig. 13 shows their development in M, polymorpha. II MUSCINE^— HEPATIC AL— MARCH ANTI ALES 45 One of the surface cells of the bottom of the receptacle projects as a papilla above the surface, and is cut off by a transverse wall from the cell below. The outer cell next divides again by a transverse wall into a lower cell, which develops no further, and a terminal cell from which the gemma is formed. This terminal cell first divides into two equal cells by a cross-wall (Fig. 13, B), and in each of these cells a similar wall arises, so that the young gemma consists of four nearly A. Fig. 13. — Marchantia polymorpha. A, Plant with gemma cups {k, k), X2; B-F, development of the gemmae, X525; G, an older gemma, X260; v, v', the two growing points. equal superimposed cells (Fig. 13, D). The wall III in Fig. 13, D, arises a little later than wall II, and is always more or less decidedly concave upward. Each of the four primary cells of the gemma is divided into two by a central vertical wall, and this is followed by periclinal walls in each of the resulting cells. At first the gemma is but one cell in thickness, but later walls are formed in the central cells parallel to the sur- face, so that it becomes lenticular. As it grows older there 46 MOSSES AND FERNS chap. is established on opposite sides (Fig. 13, G, v, v') the grow- ing points, which soon begin to develop in the manner found in the older thallus, and come to lie in a depression, so that the older gemmae are fiddle-shaped. The gemma stands vertically, and there is no distinction of dorsal and ventral surfaces. The cells contain chlorophyll, except here and there the cells with oil bodies, and an occasional large colourless superficial cell. Among them are small club-shaped hairs, wdiich secrete a mucilage that swells up when wet, and finally tears away the gemmae from their single-celled pedicels. The further development of the gemmae depends upon their position as to the light. Whichever side happens to fall down- ward becomes the ventral surface of the young plant, and the colourless cells upon this surface grow out into the first rhi- zoids. The two growing points persist, and the young plant has two branches from the first, growing in exactly opposite directions. As soon as it becomes fastened to the ground the dorsiventrality is established, and upon the dorsal surface the special green lacunar tissue and the epidermis with its charac- teristic pores are soon developed, while the ventral tissue loses its chlorophyll, and soon assumes all the characters found in the mature thallus. The branching of the thallus is in most cases dichotomous, as in Riccia, but occasionally, as in Targionia (Fig. i, E), the growth is largely due to the formation of lateral adventitious branches produced from the ventral surface. In structure and development the sexual organs correspond closely to those of the Ricciaceae, but they are always formed in more or less distinct groups or "inflorescences." As might be expected, this is least marked in the lower forms, especially the Corsinieas (Leitgeb (7), vol. iv.), where the main distinc- tion between them and the lower Ricciaceae is that in Corsinia the formation of sexual organs is confined to a special region, and that the archegonia do not have an individual envelope as in Riccia, but the whole group of archegonia is sunk in a com- mon cavity, which is of exactly the same nature as that in which each archegonium is placed in the latter. In most of the Marchantieae, however, both antheridia and archegonia are borne in special receptacles, which in the case of the latter are for the most part specially modified branches or systems of branches, raised at maturity upon long stalks (Fig. 21). The II MUSCINE^—HEPA TICAl—MARCHANTIALES 47 antheridial receptacles are sometimes stalked, but inore com- monly are sessile, and often differ but little from those of the higher Ricciacese. The sporogonium shows an advance upon that of the Ricciacese by the development of a lower sterile portion, or foot, in addition to the spore-bearing portion or capsule, and in the latter there are always sterile cells, which in all but the lowest Corsinieae have the form of elaters. At maturity, also, the ripe capsule breaks through the calyptra, except in the Corsinieae, w^here, too, the sterile cells do not develop into elaters, but seem to serve simply as nourishing cells for the growing spores. The stalk of the capsule is usually short compared with that of most Jungermanniacese, and the wall of the capsule remains intact until the spores are ripe. The spores vary much in size, and in the development of the outer w^all. In Marchantia polymorpha and other species where the spores germinate promptly, the ripe spore contains chlorophyll, and the exospore is thin and slightly developed. In such cases there is no distinct rupture of the exospore, but the whole spore elongates directly into the germ-tube. In Conocephalus, where the spores are very large, the first divi- sions occur in the spores before they are scattered. In species where the spores do not germinate at once the process is much like that of Riccia, and the thick exospore is ruptured and remains attached to the base of the germ-tube. The apical growth of the Marchantiese is very much like that of Riccia. In Fimhriaria Calif ornica (Fig. 14) the apical cells seen in vertical section show the same form as those of Riccia, and the succession of dorsal and ventral segments is the same; but here the development of the ventral segments is much greater, and there is not the formation of the median ventral lamellae as in Riccia, but the two rows of ventral scales arise independently on either side of the midrib, very near the growing point, and closely overlap and completely protect the apex. The formation of the lacunae in the dorsal part of the thallus begins earlier than in Riccia, and corresponds very closely to what obtains in Ricciocarpiis. The pits are at first very narrow, but widen rapidly as they recede from the apex. In the epidermal cells surrounding the opening of the cavity, there are rapid divisions, so that the opening remains small and forms the simple pore found in this species. As in Riccio- 48 MOSSES AND FERNS CHAP. carpus, the original air-chambers become divided by the devel- opment of partial diaphragms into secondary chambers, which are not, however, arranged in any regular order, and communi- cate more or less with one another. In Targionia (Figs. i8, 19), where the archegonia are borne upon the ordinary shoots, the growth of the dorsal seg- ments is so much greater than that of the ventral ones that the upper part of the thallus projects far beyond the growing point, A. which is pushed under toward the ventral side. A similar condition is found in the archegonial receptacles of other forms, where this in- cludes the growing point of the shoot (Fig. 21). In Targionia the lacunae are formed much as in Fimhriaria, but they are shallower and much wid- er, and the pores corre- spondingly few. The as- similative tissue here re- sembles that of Mar- thantia and others of the higher forms. It is sharply separated from the compact colourless tissue lying below it, and the cells form short con- fervoid filaments more or less branched and an- astomosing, and except in the central part of the chamber united with the epidermal cells. Under the pore, however, the ends are free and enlarged with less chlorophyll than is found in other cells. All of the Marchantiese except the aberrant genera Dumor- tiera and Monoclea correspond closely to one or the other of the above types in the structure of the thallus, but in the latter the air-chambers are either rudimentary or completely absent, and the ventral scales are also wanting. Leitgeb ( (7), vi., p. 124) Fig. \^.— Fimhriaria Californica. A, Vertical sec- tion through the apex of a sterile shoot, show- ing the formation of the air-chambers ; x, the apical cell, X300; B, similar section through an older part of the thallus, cutting through a pore, X 100. n MUSCINE^— HEPATIC JE— MARCH A\'TI ALES 4Q investigated D. irrigua, whose thallus is characterised by a pecuhar areolation composed of projecting ceU i)lates, and came to the conclusion that these were the remains of the walls of the air-chambers, whose upper parts, with the epidermis, were thrown off while still very young. lie had only herlia- rium material to work with, Ixit in this he detected traces of the epidermis and pores in the younger i)arts. 1 examined with some care fresh material of D. trichocephala, from the Hawa- iian Islands, and find that in this species, whicli lias a ])erfectly smooth thallus without areolations, that no trace of air-cham- bers can be detected at any time. Vertical sections through the apex show the initial cells to be like those of other Marchan- tiaceae, and the succession of segments the same, but no indi- cations of lacunae can be seen either near the apex or farther back, the wdiole thallus being composed of a perfectly contin- uous tissue without any intercellular spaces, and no distinct limit between the chlorophyll-bearing and tlie colourless tissue. As Dinnortiera corresponds in its fructification with the higher Marchantieas, the peculiarities of the thallus are probably t(j be regarded as secondary characters, perhaps produced from the environment of the plant, and species like D. irrigua would form transitional stages between the typical Alarchantiaceous thallus and the other extreme found in D. trichocephala. Sexual Organs The structure and development of the sexual organs are very uniform among the Marchantiaceae. In Finihriaria Cali- fornica, wdiich is dioecious, the antheridial receptacle forms a thickened oval disc just back of the apex. Not infrequently (Fig. I, A), when the formation of antheridia begins not long before the forking of the thallus, both of the new growing points continue to develop antheridia for a time, and the recep- tacle has two branches in front corresponding to these. The receptacle is covered with conspicuous papilke which mark the cavities in which the antheridia are situated. Vertical longi- tudinal sections through the young receptacle show antheridia in all stages of development, as their formation, like those of Riccia, is strictly acropetal. The first stages are exactly like those of Riccia, and the primary cell divides into two cells, a pedicel and the antheridium proper. The divisions in the lower so MOSSES AND FERNS CHAP. cell are somewhat irregular, but more numerous than in Riccia, so that the stalk of the ripe antheridium is more massive (Fig. i6). In the upper cell a series of transverse walls is formed, varying in different species in number, but more than in Riccia, and apparently always perfectly horizontal. In Marchantia polymorpha Strasburger (2) found as a rule but three cells, before the first vertical walls were formed. In an undetermined species of Fimhriaria (Fig. 15) probably F. Bolanderi, the antheridia were unusually slender, and fre- quently four, and sometimes five transverse divisions are formed before the first vertical walls appear. Sometimes all the cells divide into equal quadrants by intersecting vertical walls, but quite as often this division does not take place in the uppermost Fig. 15. — Fimhriaria sp. (?). A, Part of a vertical section of a young antheiidial receptacle, showing two very young antheridia (J'), X420; B-E, older stages. and lowest cell of the body of the antheridium, or the divisions in these parts are more irregular. The separation of the cen- tral cells from the w^all is exactly as in Riccia, and the lower segments do not take any part in the formation of the sperm cells, but remain as the basal part of the wall. In Fimhriaria the top of the antheridium is prolonged as in Riccia, but in Marchantia this is not the case. The wall cells, as the anther- idium approaches maturity, are often much compressed, but in Targionia hypophylla, where Leitgeb states that this com- pression is so great that the cells appear like a simple membrane, I found that, so far from this being the case, the cells were extraordinarily large and distinct, and filled the whole space between the body of the antheridium and the wall of the cavity, which in Leitgeb's figures ((7), vi., PI. x.. Fig. 12) is repre- II MUSCINEJE— HEPATIC JE—M ARC 11 AXTI ALES 51 sented as empty. The antheridium becomes sunk in the thallus precisely as in Riccia. The sperm cells are nearly cubical and the spermatozoid is formed in the usual way. The free spermatozoid (Fig. 16, D) shows al-xjut (juc ruid a hrdf com- plete turns of a spiral. The cilia are very long-, and the vesicle usually plainly evident. According to Ikeno (4), in Marclianlia polyiiiorpJia the final division, resulting in the pair of s])ermatids, is unaccom- panied by a division wall, and this seems also to be the case in Fig. i6.—Fimbriaria Californica. A. Longitudinal section of a fully-developed male receptacle, X8; B, longitudinal section of a nearly ripe antheridium, Xioo; C, young sperm cells, X6oo; D, spermatozoids, X1200. Fimbriaria. In the earlier divisions of the sperm-cells, each cell shows two centrosomes (Fig. 17, i), and Ikeno does not recognise any difference between these and the so-called ''blepharoplast" of Webber and other recent students of sperma- togenesis, who look upon the blepharoplast as a different organ from the centrosome. After the final division, each spermatid is provided with a single centrosome (blepharoplast), from which, later, the cilia arise. 52 MOSSES AND FERNS CHAP. The young spermatid (Fig. 17, 3) is triangular in section, and the blepharoplast is situated in the acute angle which later forms the anterior end of the spermatozoid. The blepharoplast becomes somewhat elongated, and from it grow out the two cilia before any marked change is observable in the nucleus. (Fig. 17, 5). Before the cilia can be seen, there appears in the cytoplasm a round body which stains strongly, but whose origin is not clear. This body Ikeno calls the chromatoid *'Neben- korper," and says that it does not participate directly in the development of the spermatozoid, but ultimately disappears. His figures 30 and 31, however, look as if the portion of the spermatozoid between the blepharoplast and the nucleus was derived from this "nebenkorper," and not from the cytoplasm, as he states is the case. Fig. 17. — Marchantia polymorpha. Development of the spermatozoid, i, Sperm-cells from the young antheridium; 2, final division of the sperm-cell to form the two spermatids; 3-7, development of the spermatozoid; b, blepharoplast; p, "neben- korper"; (All figures after Ikeno). Owing to the very small size of the spermatozoids in Marchantia^ it could not be positively demonstrated whether there is a cytoplasmic envelope about the nuclear portion of the spermatozoid, but it was concluded that such probably is the case. When the antheridia are borne directly upon the thallus, the apical growth continues after antheridia cease to be formed, and the receptacle is thus left far back of the growing in point. In forms like Targionia, however, where there are special antheridial branches, the growth of these is limited, and gener- ally ceases with the formation of the last antheridia. The most n MUSCINEAi— HEPATIC JE— MARCH AXTI ALES 53 specialised forms are found in the genus Marcluuitia and its allies, where the antheridial receptacle is burnc up(jn a hjng stalk, which is a continuation of the branch frc^n which it grows, and the receptacle is a Ijrrnicli-systcni. 1 "he growing point of the young antheridial l)ranch fcjrks while still very young, and this is repeated in (|uick succession, so that there results a round disc with a scalloped margin, each indentation marking a growing point, and the whole structure being efjuiva- lent to such a branch system as is found in Riccia or Anthoceros, wdiere the wdiole thallus has a similar rosette-like form. 'Hie antheridia are arranged in radiating rows, the youngest (jne nearest the margin and the eldest in the centre. In S(jme tropical species, e.g., M. geminata, the branches of the receptacle are extended and its compound character is evident. The discharge of the spermatozoids from the ripe anther- idium may take place with great force. In the case of Fimhriaria Calif ornica, Peirce (i) found they were thrown vertically for more than fourteen centimetres. The mechanism involved includes not only the tissues of the antheridium itself, but also the cells below the antheridium, and those forming the vails of the chambers in which the antheridia are situated. These cells, becoming strongly distended with water, exercise great pressure upon the antheridium, whose mucilaginous con- tents are also strongly distended. The upper wall of the antheridium is finally burst, and the contents expelled violently through the narrow, nozzle-like opening of the antheridial chamber. This explosive discharge was first noted by Thuret ( i ) in Conocephahis conicus, and has been recently studied in that species by King ( i ) and Cavers ( i ) , as well as in several other genera. It is much more marked in the dioecious species. The archegonia are never sunk in separate cavities, but stand free above the surface of the thallus. The simplest form may be represented by Targionia. Here the archegonia arise in acropetal succession from the dorsal segments of the initial cells of the ordinary branches. A superficial cell enlarges and is divided as in Riccia into an outer and an inner cell. The latter undergoes irregular divisions and its limits are soon lost. In the outer cell the divisions occur in the same order as in Riccia, but from the first the base of the archegonium is broad and not tapering. Strasburger (2) states that in MarcJiantia 54 MOSSES AND FERNS CHAP. there is a division of the outer of the two primary cells by a wall parallel to the first, and that the lower one forms the foot of the archegonium, and Janczewski ( i ) gives the same account of the young archegonium of Pi'eissia commutata. This cer- tainly does not occur in Targionia, and to judge from the later stages of Fimhriaria Californica, this species too lacks this B Fig. i8. — Targionia hypophylla. A, Longitudinal section of the thallus, Xioo; ar, archegonia; / /. ventral scales; B, median section through a pore, showing the assimilating cells (c/) below, X300. division. The full-grown archegonium is of more nearly uniform thickness than in Riccia, as the venter does not become so much enlarged. The neck canal cells are more numerous, about eight being the common number, but in Targionia the formation of division walls between these is sometimes sup- II MUSCINE^— HEPATIC JE—MAKCI J AXTI ALES 55 pressed (Fig. 19, C), so that this may acojunt for Janczewski's error in stating that the number was always four, as the nuclei in unstained sections might very easily he (Aciiocjked. The cover cells are somewhat smaller than in Riccia and do not usually undergo as many divisions, there being seldom nvjre than six in all. In Targionia (hig. 23, A), and Strasburger ((21), p. 418) observed the same in MarcJiaiitia, the ripe n^^ shows a distinct ''receptive spot," that is, the upper ])art of the unfertilised egg is comparatively free from granular cyto])lasm, while the lower part, about two-thirds in Targionia, is much more densely granular. The nucleus is not very large and has very little chromatin. The nucleolus is large and distinct and / A, D Fig. 19. — Targionia hypophylla. A, Longitudinal section of the apex of the thallus, with young archegonia (ar), X525; x, the apical cell; B, young, C, older archc- gonium in longitudinal section; D, cross-section of the archegonium neck, X5-5- Stains very intensely. As the archegonium of Targioiiia matures, its neck elongates rapidly and bends forward and upward, no doubt an adaptation to facilitate the entrance of the spermatozoid. A similar curving of the archegonium neck is observed in other forms wdiere the archegonium is upon the lower side of the receptacle. After an archegonium (or sometimes several of nearly equal age) is fertilised, the growth in length of the thallus stops. 56 MOSSES AND FERNS EHAP. but there is a rapid lateral growth with results in the formation of two valves, which meet in front much like the two parts of a bivalve shall, and this involucre completely encloses the devel- oping sporogonium. In the simplest cases, where the archegonia are borne upon a receptacle^ which is raised upon a stalk, e.g.j Plagiochasma, Clevea (Fig. 20, A), the receptacle does not represent, accord- ing to Leitgeb ( (7), vi., p. 29), a complete branch, but is only a dorsal outgrowth of the latter, which may grow out beyond it, or even form several receptacles in succession. The first indi- cation of the recep- 2. A. '■jjrl'jijIlrilJUfl tacle is a dorsal prom- inence which soon be- comes almost hemi- spherical, and near the _ ^.^ V. hinder margin the first archegonium arises, without, apparently, any special relation to the growing point. On the lateral margins are then formed two other archegonia, not, however, simultane- ously; and finally a fourth may be formed in front : three or four archegonia in all seem to be the ordinary ^ ^, . A 1 •. ^- 1 .• f number. The stalk of Fig. 20. — A. Clevea sp. A, longitudinal section of . ^ the thallus showing the dorsal origin of the fe- thc rCCCptaclc IS alSO male receptacle (J) ; v, the growing point (dia- ^ dorSal aOOenda2"e of gram after Leitgeb) ; B, Reboulia hemisphcerica ^^ ° (Radd.), longitudinal section of very young re- tllC tlialluS, and nOt 3. ceptacle with the first archegonium C^) ; x, the rl i r- p p f COUtinUation apical cell, X300 (after Leitgeb). of it. The next type is that which Leitgeb attributes to Grim al dia, Reboulia, Fimbriaria, and some others, but it is not the type found in Fimbriaria Calif arnica. In this type the structure of • The sporongonial receptacle of the Alarchantiese is sometimes known as the Carpocephalum. MUSCINE^—HEPA TIC^— MARCH ANTI ALES 57 the receptacle and the origin of the archegonia are the same ^s in that just described; but here the growing point of the A B. sp per ' \^ D Fig. 21. — Fimhriaria Calif ornica. A, Plant with two fully-grown sporogonial recep- tacles, natural size; B, single receptacle, X4; C, the same cut longitudinally, showing the sporogonium {sp), enclosed in the perianth {per); D, nearly median section of a young receptacle, showing one growing point (x) and an arche- gonium {ar) ; L, air-spaces; st, a pore; r, rhizoids, X40; E, the growing point of the same with an archegonium, X300; x, the apical cell. branch forms the forward margin of the receptacle, and the stalk is a direct continuation of the axis of the branch. Upon 58 MOSSES AND FERNS chap. its ventral surface it shows a furrow in which rhizoids are produced in great numbers, and this furrow continues along the ventral surface of the thallus. The highest type is that of Leitgeb's "Compositse." In this form the female receptacle is a branch system similar to that of the male receptacle of Marchantia. The branching is usually completed at a very early period, while the receptacle is almost concealed in the furrow in the front of the thallus. A simple case of this kind is seen in Fimbriaria Calif ornica (Fig. 21). In this case there are four growing points that have arisen from the repeated dichotomy of the primary growing point of the branch, and each of these gives rise to archegonia in acropetal succession, much as in Targionia, but the number of archegonia is small, not more than two or three being as a rule formed from each apex. The development of the dorsal tissue is excessive and the ventral growth reduced to almost nothing, and the growing apices are forced under and upward and lie close to the stalk, and the archegonia have the appearance of being formed on the ventral side of the shoot, although morphologic- ally they are dorsal structures. In the common Marchantia polymorpha the branched character of the receptacle is empha- sised by the development of the ''middle lobe" between the branches. These lobes grow out into long cylindrical appendages between the groups of archegonia, and give the receptacle a stellate form. Usually in M. polymorpha there are eight growing points in the receptacle, and of course as many groups of archegonia, which are more numerous than in any other genus, amounting to a hundred or more in one recep- tacle. In Marchantia, as well as some other genera with com- pound receptacles, there are two furrows in the stalk, showing that the latter is influenced by the first dichotomy. While the archegonia, before fertilisation, are quite free, the whole group of archegonia, and indeed the whole receptacle, is invested with hairs or scales of various forms that originate either from the epidermis of the dorsal side, or as modifications of the ventral scales. The peculiar American genus Cryptomifritini has been investigated by Abrams ( i ) and Howe (3), who finds the devel- opment of the carpocephalum to agree essentially with that of Fimbriaria Calif ornica. Cavers (6, 7, 8), has recently investi- gated that of Conocephahis (Fegatella), Reboulia and Preissia. II MUSCINE^—HEPA TIC Al— MARCH ANTI ALES 59 The lacunar tissue is very much develoijed upon the receptacles, as are to an especial degree the peculiar cylindrical breathing pores. The formation of these begins in the same way as the simple ones, being merely tlic original opening to the air-space. This seen from the surface shows an opening with usually five or six cells surrounding it. Vertical sections show that very soon the cells surrounding the pore become deeper than their neighbours and project both above and below them. In these cells next arise (Fig. 11, A, B) a series of inclined walls by which each of the original cells is transformed into a row of several cells, and these rows together form a curious barrel-shaped body surrounding the pore. The upper cells converge and almost close the space above, and this is still further diminished by the cuticle of the outer cell wall of the uppermost cells growing beyond the cells and leaving simply a very small central opening. The rows of cells also converge below, and in Fiinhriaria Calif ornica the lowermost cells are very much enlarged, and probably serve to close the cavity completely at times, and act very much like the guard cells of the stomata of vascular plants. In Leitgeb's group of the Astroporge, the simple pores of the thallus have the radial walls of the surrounding cells strongly thickened, so that the pores seen from the surface appear star-shaped. The most special- ised of the Marchantiese, i. e., Marchantia, Preissia, etc., have the cylindrical pores upon the vegetative part of the thallus as well as upon the receptacle, but in the others they occur only upon the latter. The Sporophyte. The first divisions in the embrvo of the Marchantiacese and Corsiniaceae are the same as in the Ricciacese, but only the upper part (capsule) of the sporogonium develops spores, while the rest becomes the stalk and foot. The simplest form of capsule is found in the genera Corsinia and Boschia, which have been carefully studied by Leitgeb ((7), iv., pp. 45-47). In these the embryo, instead of remaining globular as it does in Riccia, elongates and very early becomes differentiated into a nearly globular upper part, or capsule, and a usually narrower basal portion, the foot (Fig. 22). In the capsule at a very early period a single distinct layer of outer cells is separated from the central group of cells, and forms the wall of the 6o MOSSES AND FERNS - chap. capsule, which in Boschia at maturity develops upon the inner cell walls thickened bars. Only a portion of the cells of the central part produce spores ; the remainder do not divide after the spore mother cells are formed, but remain either as simple slightly elongated nourishing cells (Corsmia) or elaters (Boschia). The other Marchantiacese are much alike, and as Targionia was found to be an especially satisfactory form for study, on account of the readiness with which straight sections of the embryo could be made, it was taken as a type of the higher Marchantiales. The first division wall (basal wall) is trans- verse, and divides the embryo into two nearly equal parts. This is followed in both halves by nearly vertical walls (quadrant walls), and these and the basal wall are then bisected by the octant walls, so that as in Riccia the young embryo is formed of eight nearly equal cells. In Targionia, even at this period, the embryo is always somewhat elongated instead of globular. The next division walls vary a good deal in different individuals. Fig. 23, C shows a very regular arrangement of cells, where the first divisions were much the same in all the quadrants. Here all the secondary walls were nearly parallel with the basal wall, and intersected the quadrant and octant walls ; but quite as often, especially in the upper half of the embryo, these secondary walls may intersect the basal wall. In no cases seen was there any indication of a two-sided apical cell such as Hofmeister figures for Tar- FiG. 22. — Corsinia inarch an- . . , 111 1 • tioides. Young sporogo- gwuia, and probably his error arose nium, optical section. X300 from a study of forms where the quad- ^' ^^ ' rant walls were somewhat incHned, in which case the intersection of one of the secondary walls with it might cause the apex of the embryo to be occupied by a cell that, in section, would appear like the two-sided apical cell of the Moss embryo. The regular formation of octants was ob- served by me in Fimhriaria Calif ornica, and by Kienitz-Gerlofif n MUSCINE^— HEPATIC JE— MARCH ANTI ALES 6i (i, 2) and others in Marchantia, Grwialdia, and Prcissia, and probably occurs normally in all Marchantiaceae. After the tirst anticlinal walls are formed in the octants, no Fig. 23. — Targionia hypophylla. A, Longitudinal section of the venter of a ripe archegonium, Xsoo; B-E, development of the embryo, seen in longitudinal median section — B, two-celled, D, four-celled stages, X500 except E, which is magnified 150 times; F, median section of the upper part of an older embryo, X250. definite order could be observed in the succeeding cell divisions, especially in the lower half of the embryo. In the upper part 62 MOSSES AND FERNS :hap. periclinal walls appear, but not at any stated time, so far as could be made out, and the first ones do not, as Leitgeb asserts, necessarily determine the separation of the archesporium, as in the Corsiniese. The growth now becomes unequal, the cells in the central zone not dividing so actively, a marked constriction is formed, and the young sporogonium becomes dumb-bell shaped. By this time a pretty definite layer of cells (Fig. 27,, F) is evident upon the outside of the capsule, but the cells of the globular lower part, or foot, are nearly or quite uniform. They are larger than those of the capsule, and more transparent. Gal. Fig. 24. — Targionia hypophylla. A, Median longitudinal section of older embryo enclosed in the calyptra (cal), X8o; B, a portion of the upper part of the same embryo, X480; the nucleated cells represent the archesporium; C, part of the archesporium of a still later stage; el, elaters; sp, sporogenous cells, X480. In the latter the wall becomes later more definite, and remains but one cell thick until maturity. The arrangement of the cells of the archesporium is very irregular, and until the full number of these is formed they are all much alike. Just before they separate, however, careful observation shows that two well- marked sorts of cells are present, but intermingled in a perfectly irregular way A part of these cells are nearly isodiametric, the others slightly elongated, and the nuclei of the former cells II MUSCINE^— HEPATIC Ai— MARCH ANTI ALLS 63 are larger and more definite than those of the latter. At this stage the cells hegin to separate by a partial deliquescence of their cell walls, and when stained with Bismarck-brown these mucilaginous walls colour very deeply, and the cells are very distinct in sections so treated. They finally separate com- pletely, and the much-enlarged globular capsule now contains a mass of isolated cells of two kinds, globular sporogenous cells and elongated elaters. The former now divide into four spores, but before the nucleus divides the division of the spores is indicated by ridges which project inward and divide the cavity of the mother cell much as in the Jungermanniaceae. With the first divisions in the embryo the venter of the Fig. 25. — Fimbriaria Californica. A, Young, B, older embryo in median section. A, X300; B, Xioo; C, upper part of a sporogonium, after the differentiation of the archesporium, X200. archegonium, which before was only one cell thick, divides by a series of periclinal walls into two layers of cells, which later undergo further divisions, so that the calyptra surrounding the older capsule may consist of four or more layers of cells. The neck of the archegonium remains unchanged, but the tissue of the thallus below the archegonium grows actively, and sur- rounds the globular foot, which has grown down into the thallus for some distance, and only the capsule remains within the calyptra. This large growth of the foot is at the expense of the surrounding cells of the thallus, which are destroyed by its 64 MOSSES AND FERNS CHAP. growth, and through the foot nourishment is conveyed from the thallus to the developing capsule. That is, the sporogo- nium is here a strictly parasitic organism, growing entirely at the expense of the thallus. The further grow^th of the spores and elaters was studied in Fimbriaria Calif ornica. The spores remain together in tetrads, until nearly ripe. In sections parallel to the surface of the younger spores (Fig. 26, C) the outer surface of the exospore is covered with very irregular sinuous thickenings, at first projecting but little above the surface, but afterward becoming in this species extraordinarily developed. In sections of the D. FiG. 26. — Fimbriaria Californica. A, Young elater X6oo; B, a fully-grown elater, X300; C, surface view of the wall of a young spore, showing the developing episporic ridges, X6oo; D, section of a wall of a ripe spore, X300. ripe spore (Fig. 26, D) three distinct layers are evident, the cellulose endospore, the thick exospore, and this outer thick- ened mass of projecting ridges which has every appearance of being deposited from without, and must therefore be charac- terised as epispore (perinium) ; Leitgeb ((7), vi., p. 45) dis- tinctly states that thickenings of this character do not occur in the Marchantieae, but that the thickenings are always of the character of those in Riccia. II MUSCINEAi— HEPATIC JE— MARCH AXTI ALES 65 The elaters are at first elongated tliin-w ailed cells with a distinct although small nucleus, and ncarl\ uniformly granular cytoplasm. As they grow the cytoplasm loses this unif(jrm appearance, and a careful examinaticju, especially of sections, shows that the granular part of the cytoplasm begins to form a spiral band, recalling somewhat tlie chloro])hyll band of Spirogyra. This is the beginning of the characteristic spiral thickening of the cell wall, and while at first irregular, the arrangement of the granular matter becomes more definite, and following the line of this spiral band of granules in the cyto- plasm, there is formed upon the inner surface of the wall the regular spiral band of the comi)lete elater. Hiis band, which is nearly colourless at first, becomes yellow in the mature elater, and in Targionia, wdiere there are generally two, they are almost black. Not infrequently branched elaters are found, but these are unicellular, and no doubt owe their peculiar form to their position between the spore mother cells in the young archesporium. An axial row^ of granules, which seem to be of albuminous nature, remains in the elaters of Fiuihriaria until maturity. The differences in the structure of the sporogonium in different genera of the Marchantieae are slight. In Marchantia polymorpJia, the young sporogonium is nearly globular, and even when full grown it is ellipsoid with the stalk and foot quite rudimentary. Most forms, however, have the foot large, but the stalk, compared w^ith that of most Jungermanniace?e, is short. In most of them the wdiole of the upper half of the young embryo develops into the capsule, but in Fiuihriaria Calif ornica I found that the archesporium was smaller than in other forms described, and that sometimes the apical part of the sporogonium w^as occupied by a sort of cap of sterile cells (Fig. 25, C). When ripe, the cells of the capsule-wall in Targionia de- velop upon their walls dark-colored annular and spiral thicken- ings much like those of the elaters. These thickenings are quite w^anting in Fimhriaria. The dehiscence of the capsule is either irregidar. e.g.. Targionia, or by a sort of lid, e.g., Grimaldia, or by a number of teeth or lobes, e.g., Liinnlaria, Marchantia. In some forms after fertilisation there grows up about the archegonium a cup- shaped envelope, "perianth, pseudoperianth," which in Fini- 6 ^ MOSSES AND FERNS CHAP, briaria especially is very much developed, and projects far beyond the ripe capsule (Fig. 21). The germination of the spores corresponds in the main with that of Riccia. Except in cases where the exospore is very thin, in which case it is not ruptured regularly, the exospore either splits along the line of the three converging ridges upon Fig. 27. — Targionia hypophylla. Germination of the spores, X about 200. In B two germ tubes have been formed; C and E are optical sections; x, apical cell; r, primary rhizoid; sp, spore membrane. the ventral surface, and through this split the endospore pro- trudes in the form of a papilla, as in Riccia; or in Targionia (Fig. 27) the exospore is usually ruptured in two places on opposite sides of the spore, and through each of these a filament protrudes, one thicker and containing chlorophyll, the other more slender and nearly colourless. The first is the germ tube, the second the first rhizoid. In Fimhriaria Californica the first rhizoid usually does not form until a later period. In Targionia a curious modification of the ordinary process is quite often met with (Fig. 27, B). Here, by a vertical divi- sion in the very young germ tube, it is divided into two similar cells, which both grow out into germ tubes. Whether both of these ever produce perfect plants was not determined, but the first divisions in both were perfectly normal. The first divisions in the germ tube are not quite so uniform as in II MUSCINE^—HEPA TIC JE— MARC HAN TI ALES 67 Riccia trichocarpa, but resemble them very closely In the com- moner forms. In Fiinhriaria especially, and this has also been observed in Marchantia (Leitgeb (7), vi., PL ix., Fig. 13) and other gen- era, a distinct two-sided apical cell is usually developed at an early period, and for a time the growth of the young plant is due to the segmentation of this single cell. Finally this is replaced by a single four-sided cell (Fig. 29, C), very much like the initial cell of the mature thallus. The young plant, composed at first of homogeneous chlorophyll-bearing cells, grows rapidly and develops the characteristic tissues of the older thallus. The first rhizoids are always of the simple form, and the papillate ones only arise later, as do the ventral scales. Tar- gionia shows a number of pe- culiarities, being much less uniform in its development than Fimhriaria. While it often forms the characteristic germ tube, and the divisions there are the same as in Riccia and Fimhriaria, the formation of a germ tube may be com- pletely suppressed, and the Fig. 2S.—Targionia hypophylla. Germ flj-St rCSUlt of gCrmiuatioU is plant in which the thallus (T) has ^ - , . , been formed secondarily, X260. Often a CCll maSS, from whlCh later a secondary germ tube may be formed with the young plant at the apex (Fig. 28). Such cases as these are the only ones where it seems really proper to speak of the plant arising secondarily from a proto- nema, for in other cases, as in Riccia, the growth is perfectly continuous, and the axis of the young thallus is coincident with that of the germ tube, and in no cases observed by me could it in any sense be looked upon as a secondary lateral growth. Biology of the Marchantiaceae While the Marchantiaceae are, as a rule, moisture-loving plants, still some of them are markedly xerophilous. Most of the commoner Calif ornian species, e.g., Fimhriaria Calif ornica, Targionia hypophylla, Cryptomitriiim tencnim, dry up com- Fig. 29. — Fimhriaria Calif ornica. A, B, Young plants in optical section, showing the single two-sided apical cell (x), X260; C, horizontal section of an older plant with a single four-sided initial {x), X42S; D, E, two young plants, D from below, E from the side, X8s. II MUSCINE^— HEPATIC JE— MARCH ANTI ALES 69 pletely during the long rainless summer, and revive imme- diately with the advent of the autumn rains. In these species, the growing point of the thallus, with a good deal of the adjacent tissue, survives, and at once becomes fresh and active. The scales and mucilage-cells found about the apex are doubt- less water conservers, and according to Cavers (3, 6, 7), the tuberculate rhizoids are also concerned in holding water. In Fimbriaria Calif ornica, even the young antheridia survive the long summer drought. It has been shown (Cavers (6, 7)), that the large hyaline cells terminating the green assimilating filaments in the air- chambers of such forms as Conoccphalus and Targionia are the principal agents in the transpiration of water from the under- lying tissues. Besides the formation of definite gemmae like those of Marchantia and Lumilaria, the thallus in most Marchantiaceae is capable of extensive regeneration, even from small frag- ments. In Conoccphalus there have also been found tuberous outgrowths, which are formed under certain conditions and are doubtless for propagation (Cavers (6)). The Marchantiaceae are readily separable into two sub- families, the Targioniese, and the Marchantiese. Leitgeb has made a further division of the latter family, but some of the characters given are not sufficiently constant to warrant his division, and for that reason it has been thought best not to accept them. Thus Fimbriaria Calif ornica, which is, in regard to its fructification, typical, has the female receptacle of the composite type, a character which, according to Leitgeb, not only does not belong to the genus Fimbriaria, but is not found in any genus of the group (Operculatcc) to which he assigns it. This species too does not have the capsule opercu- late, but opens irregularly. The Targioniese include the two genera Targionia, which has been already described at length, and CyatJwdium (Leitgeb (7), vi., p. 136), whose development is not sufficiently known to make its systematic position quite certain. In the position of the sexual organs, and the formation of the two-valved involucre about the fruit, as well as the position of the latter, it corresponds closely to Targionia, but the structure of the thallus is extraordinarily simple, there being practically but two layers of cells with large irregular air-chambers between. While two 70 MOSSES AND FERNS chap. sorts of rhizoids are present, those that represent the papillate type of the other Marchantiacese, while thicker walled than the others, do not develop the projecting prominences. Indeed the whole structure of the plant is curiously reduced, and Leitgeb describes it as resembling the young plants of Mar- chantia or Preissia. The development of the sexual organs is but imperfectly known, and the suggestion of Leitgeb's that possibly the antheridium is reduced to a single cell, seems hardly probable in view of the structure of the rest of the plant. The sporogonium has the stalk and foot exceedingly rudimentary, but the upper part of the capsule shows a zone of cells whose walls are marked by peculiar ring-shaped thickenings, and opens regularly by a number of teeth, which on account of the thick- ened bars upon the cell wall offer a superficial resemblance to the peristome of the Bryales. As in Targionia the archegonia arise near the apex of the ordinary shoots, and no proper receptacle is formed. All of the other forms have the archegonia borne upon a special receptacle, which, as the sporogonia develop, is raised upon a stalk. Here belong, according to Schiffner ( i ) sixteen genera with about 150 species. The receptacle may be, as we have seen, strictly dorsal in origin, or it may include the grow- ing point of the archegonial branch, or finally it may be a branch system arising from the repeated dichotomy of the original growing point. MONOCLEA The genus Monoclea includes two known species, M, Forsteri, found in New Zealand and Patagonia, and M, Gottschei, of Tropical America, said also to occur in Japan. This genus has been usually associated with Jungermanniales (Leitgeb (7), vol. iii., Schiffner (i)), but a more complete study of the plant has shown that its affinities are undoubtedly more with the simpler Marchantiacese. The structure and posi- tion of the sexual organs, especially the antheridia, and the development of the sporophyte, so far as it has been made out (Cavers (7), Johnson (3)), all point unmistakably to a rela- tionship with the Marchantiacese. Two kinds of rhizoids are present, although not so marked as in the typical Marchantiacese, but the thallus lacks the char- II MUSCINEJE—HEPA TIC^— MARCH ANTI ALES 71 acteristic lacunar tissue of these forms. In the latter respect Monoclea closely resembles Diimortiera, and as in that genus, the absence of the air-chambers may be attributed to the semi- aquatic habit of the plant. Monoclea evidently belongs to the lower series of Marchantiaceae, and may perhaps be compared to Targionia. See Ruge (i), Cavers (7), Campbell (19). Resume of the Marchantiales Comparing the different members of this order, one is struck by the almost imperceptible gradations in structure between the different families, and this accounts for the difference of opinion as to where certain genera belong. That the Ricciacese cannot be looked upon as a distinct order is plain, and they may perhaps be best regarded as simply a family co-ordinate with the Cor- siniese and Targionieae, and not a special group opposed to all the other Marchantiaceae. The gradual increase in complexity of structure is evident in all directions. First the thallus passes by all gradations from Riccia — with its poorly defined air- chambers with no true pores and single ventral lamellae, through Ricciocarpiis and Tessalina, where definite air-cham- bers are present, opening by pores of the same form as those of the lower Marchantieae, and separate ventral scales occur — to forms like Marchantia, where the air-chambers are verv definite and contain a special assimilating tissue, and the pores are of the cylindrical type. With this differentiation of the thallus is connected the segregation of the sexual organs and the devel- opment of special receptacles upon which they are borne. Finally, in the development of the sporogonium, while there is almost absolute uniformity in the earlier stages, we find a complete series of forms, beginning w^ith Riccia, where no stalk is developed and all the cells of the archesporium develop spores, ascending through Tessalina, with a similar absence of a stalk, but the first indication of sterile cells, through the Corsinieco, to forms with a massive foot and elaters fully developed. It may be said, however, that there is no absolute parallelism be- tween the development of the gametophyte and that of the sporophyte; for in Marchantia, the most specialised genus as to the gametophyte, the sporogonium is less developed than in the otherwise simpler Targionia and Fimbriaria. CHAPTER III THE JUNGERMANNIALES A VERY large majority of the Hepaticse belong to the Jungermanniales, which show a greater range of external dif- ferentiation than is met with in the Marchantiaceae, but less variety in their tissues, the whole plant usually consisting of almost uniform green parenchyma. In the lowest forms, e.g., Aneiira and Metzgeria, the gametophyte is an extremely simple thallus, in the former composed of almost perfectly similar cells, in the latter showing a definite midrib. Starting with these simplest t3^pes, there is a most interesting series of transi- tional forms to the more specialised leafy ones, where, however, the tissues retain their primitive simplicty. All of the Junger- manniales grow from a definite apical cell, which differs in form, however, in different genera, or even in different species of the same genus. Rhizoids are usually present, but always of the simple thin-walled type. The gametophyte, with the exception of the genera Haplo-. mitrium, and Calohryum, is distinctly dorsiventral, and even when three rows of leaves are present, as in most of the foliose forms, two of these are dorsal and lie in the same plane, while the third is ventral. In the thallose forms, while the bilaterality is strongly marked, there is not the difference between the tissues of the dorsal and ventral parts which is so marked in the Marchantiales. In the lowest forms the gametophyte is a simple flat thallus fastened to the substratum by simple rhizoids, and develops no special organs except simple glandular hairs which arise on the ventral side near the apex, and whose muci- laginous secretion serves to protect the growing point. In Blasia and Fossomhronia we have genera that while still retain-^ ing the flattened thalloid character, vet show the first formation 73 Ill ^ THE JUNGERMANNIALES 73 of lateral appendages which represent the leaves of the true foliose forms. In the latter the axis is slender, and the leaves usually in three rows and relatively large. The archegonia correspond closely in their development to those of the Marchantiaceae, and in tlie lower (anacrogynous) forms arise in much the same way from surface cells of the dorsal part of the younger segments, and the apical cell is not directly concerned in their formation. The archegonia in these thus come to stand singly or in groups upon the dorsal surface of the thallus, wdiose growth is not interrupted by their develop- ment. In the higher leafy forms (Jungermanniacese acro- gynae) they occur in groups at the end of special branches, whose apical cell finally itself becomes the mother cell of an archegonium, and with this the growth in length of the branch ceases. The antheridia in most cases dififer essentially in their first divisions from those of the Marchantiaceas. After the first division in the mother cell, by wdiich the stalk is cut off from the antheridium itself, the first wall in the latter, in all forms inves- tigated except Sphcerocarpus, Riella and Geothallus, is vertical, instead of horizontal, and the next formed walls are also nearly vertical. The ripe antheridium is usually oval in outline and either nearly sessile or provided with a long pedicel. The spermatozoids are as a rule larger than in the Marchan- tiales, and show more numerous coils, but like those of the lat- ter, are always biciliate. The embryo differs in its earliest divisions from that of the Marchantiacege. The first transverse wall divides the embryo into an upper and lower cell, but of these the lower one usually takes no further part in the development of the sporogonium, but either remains undivided or divides once or twice to form a small appendage to the base of the sporogonium. In the upper cell the first wall may be either vertical {e. g., P cilia and most anacrogynous forms), or it may be transverse. From the upper of the two primary cells not only the capsule but the seta and foot as well are formed. The development of these differ- ent parts varies in different forms, and will be taken up when considering these. .. - All of the Jungermanniales, except the Anelatereae, possess perfect elaters, but in the latter these are represented merely by sterile cells that probably serve simply for nourishing the grow- 74 MOSSES AND FERNS chap. ing spores. The sporogonium remains within the calyptra until the spores are ripe, when by a rapid elongation of the cells of the seta it breaks through the calyptra, which is left at its base, and the capsule then opens. The opening of the capsule is usually effected by its walls splitting into four valves along lines coincident with the first formed vertical cell walls in the young embryo. These valves, as well as the elaters, are strongly hygroscopic, and by their movements help to scatter the ripe spores. The latter show much- the same differences observed in the Marchantiaceae. When the spores germinate at once they have abundant chlorophyll and a thin exospore, but where they are exposed to drying up, they have no chlorophyll and the exospore is thick and usually with characteristic thick- enings upon it. From the germinating spore the young gametophyte may develop directly, or there may be a well- m.arked protonemal stage. This latter is always found in the foliose forms, and is either a flat thallus, like the permanent condition of the lower thallose genera, or sometimes (Proto- cephalozia) it is a branched filamentous protonema, very much like that of the Mosses, and sometimes long-lived and produc- ing numerous gametophores. Non-sexual reproductive bodies in the form of unicellular gemmae are found in many species, and in Blasia special receptacles with multicellular gemmae something like those of Marchantia occur. The Jungermanniales naturally fall into two well-marked series,^ Anacrogyn^e and Acrogynae, based upon the position of the archegonia. These in the former are never produced directly from the apical cell of a branch, in the latter group the apical cell of the archegonial branch always sooner or later becomes transformed into an archegonium. The Haplomitriese show some interesting intermediate forms between the two groups, but all the other Jungermanniales examined belong decidedly to one or the other. As a rule the Anacrogynae are thallose (the "frondose" forms of the older botanists), but a few genera, especially Fossomhronia, show a genuine formation of leaves. All the Acrogynae have a distinct slender stem with large and perfectly developed leaves. ' Prof. L. M. Underwood proposes the name Metzgeriaceas fOr the Ana- crogynse, reserving the name Jungermanniaceae for the Acrogynae. These two groups he considers co-ordinate with the Marchantiales and Antho- cerotes. Ill THE JUNGERMANNIALES 75 ANACROGYN^ Jungermannlales Anacrogynae. Apical cell of female axis never becoming transformed into an archegonium. A. Anelatereae. No true elaters, but sterile cells repre- senting these. Capsule cleistocarpous. Four genera, T hallo car pus, Sphcerocarpus, Riella, Gcothallus. B. Elatereae. Capsule opening either by four valves or irregularly. Elaters always developed. a. Gametophore always dorsiventral, either strictly thallose or with more or less developed leaves. Fam- ilies, — Metzgerieae, Leptothecese, Codoniese. b. Gametophore upright with three rows of radially ar- ranged leaves. Fam. I., Haplomitrieae. Anelatere^ The simplest form belonging here is Sphcerocarpus, a genus that shows certain affinities with the Ricciacese, but on the whole seems to be more properly placed at the bottom of the series of the Jungermannlales. Sphcerocarpus terrestris occurs in Europe and the south- eastern United States. In California it is replaced by two species, 6^. Calif orniciis and S. cristatits, which until recently (Howe (3)) were not recognised as distinct, and were con- sidered to be a variety of S. terrestris. They are small plants growing upon the ground, usually in crowded patches, where, if abundant, they are conspicuous by the bright green colour of the female plants. The males are very much smaller, often less than a millimetre in diameter, and purplish in colour, so that they are easily overlooked. The thallus is broad and passes from an indefinite broad midrib into lateral wings but one cell in thickness (Fig. 30). The forward margin is occupied by a number of growing points formed by the rapid dichotomy of the original apex, and separated only by a few rows of cells. From the lower side of the thallus grow numerous rhizoids of the thin-walled form. The whole upper surface is cov- ered with the sexual organs, each of which is surrounded by its own very completely developed envelope. A vertical section passing through one of the growing points (Fig. 30, C) shows a structure closely like a similar section of Riccia. The apical cell {x) produces dorsal and 1^ MOSSES AND FERNS CHAP. ventral segments, and from the outer cells of the former the sexual organs arise exactly as in Riccia. On the ventral sur- face the characteristic scales of Riccia are absent, and are re- placed by the glandular hairs found in most of the anacrogy- nous Jungermanniales. The development of the archegonium shows one or two peculiarities in which it differs from other Hepaticse. The mother cell is much elongated, and the first division wall, by c $ Fig. 30. — Sphcerocarpus Californicus (?). A, Male plant, X40; ^, antheridia; B, median section of a similar plant, X80; C, the apex of the same section, X240; h, ventral hair. which the archegonium itself is separated from the stalk, is some distance above the level of the adjacent cells of the thallus, so that the upper cell is very much smaller than the lower one. The upper cell has much denser contents than the lower one, which instead of remaining undivided as in Riccia, divides into two nearly equal superimposed cells, this division Ill THE JUNGERMANNIALES 77 taking place about the same time as the first division in the archegonial cell (Fig. 31, B). The divisions in the latter are the same as in Riccia, and the general structure of the arche- gonium offers no noteworthy peculiarities. The number of neck canal cells is small, probably never exceeding four, and in this respect recalls again Riccia. The central cell is relatively large, and the ventral canal cell often nearly as large as the Qgg. As the archegonium develops, its growth is stronger on the posterior side, and it thus curves forward. At first the young archegonium projects free above the surface, but pres- FiG. 31. — Sphcrrocarpus sp. (?). Development of the archegonium. A-C, Longi- tudinal sections, X6oo; D, X300. ently an envelope is formed about it exactly as in Riccia, but arising at a later stage. After this has begun to form, its growth is very rapid, and it soon overtakes the archegonium and grows beyond it, and finally forms a vesicular body, plainly visible to the naked eye, at the bottom of which the arche- gonium lies. The formation of this involucre is quite inde- pendent of the fertilisation of the archegonium, and as these peculiar vesicles cover completely the whole dorsal surface of the plant, they give it a most characteristic appearance. Usu- ally each archegonium has its own envelope, but Leitgeb ( (7), 78 MOSSES AND FERNS chap. iv., p. 68) states that two or even more may be surrounded by a common envelope. When ripe, the venter of the arche- gonium is somewhat enlarged, but not so much as in Riccia. The egg-cell is very large, oval in form, and nearly fills the cavity of the single-layered venter. The first wall in the embryo is transverse, and divides the egg cell, which before division becomes decidedly elongated, into two nearly equal cells. Ordinarily in each of these cells similar transverse walls are formed before any vertical walls appear, so that the embryo consists of a simple row of cells. As in the Marchantiaceae the first wall separates the future capsule from the stalk, and in this respect Sphcerocarpus approaches the Marchantiales rather than the Jungermanni- ales. Following the transverse walls there are formed in all the upper cells nearly median vertical ones, which are inter- sected by similar ones at right angles to them, so that in most cases (although this is not absolutely constant) the upper half of the young sporogonium at this stage (Fig. 32, A) consists of two tiers, each consisting of four cells. The lower part of the embryo is pointed, and the basal cell either undergoes no further division or divides but once by a transverse wall, and remains perfectly recognisable in the later stages (Fig. 32, B, C). The other cells of the lower half divide much like those of the upper half, but the divisions are somewhat less regular. There next arise in all the cells of the upper half periclinal walls, which at once separate the wall of the capsule from the archesporium. This wall in the later stages (Fig. 32, C, D) is very definite, and remains but one cell thick up to the time the sporogonium is mature. The further divisions in the capsule are without any apparent order, and result in a perfectly glob- ular body composed of an outer layer of cells enclosing the archesporium, which consists of entirely similar cells with rather small nuclei and dense contents. While these changes are going on in the capsule, the lower part of the embryo loses its originally pointed form, and the bottom swells out into a bulb (the foot), which shows plainly at its base the original basal cell of the young embryo. This bulb is characterised by the size of the cells, which are also more transparent than those of the other parts of the embryo. Owing to the development of the stalk of the archegonium, after fertilisation the whole embryo remains raised above the Ill THE JUNGERMANNIALES 79 level of the thallus, instead of penetrating into it, as is usually the case. The stalk or portion between the capsule and foot remains short, and in longitudinal section shows about four D. Fig. 32. — SphcBrocarpus sp (?). A, B, Median longitudinal sections of the arche- gonium venter, with enclosed embryos, X260; C, an older sporogonium in median section, X260; D, a still later stage, showing the large space between the arche- sporial cells and the wall, X8s. rows of cells. As the calyptra grows the upper part becomes divided into two layers, the part surrounding the foot into three. Instead of breaking through the calyptra at maturity, 8o MOSSES AND FERNS chap. the capsule grows faster than the calyptra long before it is mature, and the upper part of the calyptra is first compressed very much and finally completely broken through by the en- larging capsule. Leitgeb calls attention to the fact that soon after the cells of the archesporium begin to separate, the whole mass of cells becomes completely separated from the wall of the capsule, which grows rapidly until the cavity w^ithin is much larger than the group of archesporial cells, which thus float free in the large cavity. Fig. 32, D shows a section through a sporogonium at this stage. The cells making up the central mass are apparently alike, but in the living sporogonium part of the cells have abundant starch and chlorophyll, while in the others these are wanting or present in much less quantity, while their place is taken by oil, but no rule could be made out as to the distribution of the two sorts of cells. The latter are the spore mother cells, while the others are gradually used up by the developing spores. The spores in S. terrestris remain united in tetrads, and escape from the capsule by the gradual decay of its wall and of the surrounding tissue of the gameto- phyte. The male plants are very much smaller than the females, with which they grow and under which they are at times almost completely hidden. The cell walls of the antheridial envelopes are often a dark purple-red colour, and this makes them much harder to see than the vivid green female plant. The apical growth and origin of the antheridium is the same as in Riccia. The first division in the primary antheridial cell is the same as in that of the archegonium, but the basal cell is smaller, and does not divide again transversely, and takes but little part in the formation of the stalk. In the an- theridium mother cell are next formed two transverse walls, dividing it into three superimposed cells. The two uppermost divide, as in the Marchantiacese, by vertical median walls into regular octants, the lower by a series of transverse walls into the stalk, which consists of a single row of cells sunk below the level of the thallus. After the division of the body of the antheridium into the octant cells, periclinal Avails are formed in each of these, so that the body of the antheridium consists of eight central cells and eight peripheral ones, and the stalk of two cells, of which the upper one forms the base of the Ill THE JUNGERMANNIALES 8i antheridium body (Fig. 33, D). At this stage and the one preceding it SpJiccrocarpiis recalls the structure of the anther- idium of the Charace?e, although the succession of walls is not exactly the same. The divisions of the central cells are ex- tremely regular, walls being formed at right angles, so that the sperm cells are almost perfectly cubical, and the limits of the primary central cells are recognisable for a long time. The development of the antheridial envelope begins much earlier than that about the archegonium, but in exactly the same w'ay. By the time that the wall of the antheridium is formed the envelope has already grown up above its summit, and as the antheridium develops it extends far beyond it like a flask, at the bottom of which the antheridium is placed, and through whose neck the spermatozoids escape. These are A B £ Fig. 33. — Sphcerocarpus sp (?). Development of the antheridium. A-D, Median lon- gitudinal sections, X450; E, an older one, X22S', F, a spermatozoid, killed with osmic acid, X900. very much like those of the other Hepaticae, and in size exceed those of most of the Marchantiaceae, but are smaller than is usual among the Jungermanniales. Leitgeb studied the germination of the spores in ^. tcrres- tris, which remain permanently united in tetrads. He found that all the spores of a tetrad were capable of normal develop- ment, W'hich does not differ from that of Riccia or other thal- lose Liverworts. A more or less conspicuous germ tube is found at the end of which the young plant develops, one of the octants of the original terminal group of cells becoming, appar- ently, the apical cell for the young plant. The latter rapidly grows in breadth and soon assumes all the characters of the 6 §2 MOSSES AND FERNS CHAP. older plant. Leitgeb (Fig. 17, PI. IX.) shows a condition that looks as if at an earlier stage a two-sided apical cell had been present, but he says nothing in regard to this. The sexual organs appear while the plant is extremely small. Leit- geb says he observed the first indications of them on individ- uals only one millimetre in diameter, and before the first papil- late hair on the ventral surface had been formed. In the commonest Californian species, ^. cristatus the spores separate completely at maturity. The early stages of germination are like those in S. terrestris. There is usually a two-sided apical cell at first, which later is replaced by the type found in the adult thallus. ^^yi\wi^ Fig. 34. — Geoihallus tuberosus. A, Male plant, X15; B, section of female plant, X15; /. young tuber. Where there is an excess of moisture the thallus may be- come much larger than usual, this being especially noticeable in the male plants. There is often, under these conditions, a development of leaf-like marginal lobes. This excessive vegetative development of the thallus is accompanied by a marked diminution in the number of the sexual organs. (Campbell (17)). Geothallus. Evidently closely allied to Sphcerocarpus is a remarkable Liverwort, as yet found only near San Diego, in Southern Ill THE JUNGERMANNIALES 83 California (Campbell (18)). Geothallus tiiherosiis (Figs. 34, 35), differs from Sphccrocarpus in its much larger size, the development of leaf-like organs, much like those of Fos- somhronia and by the very much larger size of the spores. There are also some minor differences in the structure of the reproductive organs, the antheridia having a more massive pedicel than that of Sphccrocarpus. The plants are perennial, and at the end of the growing season the younger parts of the thallus become changed into a tuber with a thick black cover- ing. The tubers are buried in the earth during the dry season. n Fig. z^.— Geothallus tuberosus. A, Archegonium, X200; B, ripe antheridium, X about 65; C, a four-celled embryo, X200; D, ripe spore; E, sterile cells, X 100. The apex of the shoot persists and resumes growth as soon as the conditions are favorable. Riella. The peculiar genus Riella (Goebel (17), Leitgeb (7), Por- sild (i)), while it closely resembles Sphccrocarpus in the struc- ture of the reproductive organs and sporophyte, differs very much in the habit of the gametophyte. Until very recently (Howe and Underwood (3)), all the species known were from the regions adjacent to the Mediterranean, but one species has since been found in the Canary Islands, and another in the United States. They are all submersed aquatics. The thal- lus shows a cylindrical axis, from which grows a thin vertical 84 MOSSES AND FERNS CHAP. dorsal lamina or wing, which may be more or less spirally placed, owing to torsion of the axis, but this torsion was much exaggerated in the early figures of the original species, R. helicophylla. According to Goebel's investigations, the grow- ing point is formed secondarily, and this statement is con- firmed by Howe's studies. The latter writer has studied the germination of the spores and has described the formation of gemmae in R. Americana. The latest contribution to our knowledge of Riella is that of Porsild ( I ) . He confirms Howe's statements and has .JL. D. G Fig. 36.— a, D, Riella Americana; B, C, R. helicophylla; A, Apex of female plant, X8; B, C, lateral and ventral view of the growing point, Xsoo; x, apical cell; Z,, leaves. D, male plant, X I J^ ; CA, D, after Howe ; B, C, after Leitgeb.) further investigated the question of the growing point. He finds that while an apical cell is absent in the younger stages, it is formed later in normal plants. Both archegonia and antheridia resemble those of Sphcero- carpus very closely, and the structure of the sporophyte is also the same, no true elaters being developed, but instead there are simply sterile cells. Ill THE JUNGERMANNIALES 8S Elatereae Aneura and Metzgeria represent the simplest of the typical anacrogynous Jungermanniales. Jn the former the thallus is composed of absolutely similar cells, all chlorophyll-bearing, and in each cell one or more oil bodies, like those of the Mar- chantiacese. In Mctzgeria (Fig. 37) the wings of the thallus are but one cell thick, and there is a very definite midrib, usu- ally four cells thick. The apical growth in both genera is Fig. 27.—~Metsgeria pubescens. A, Surface view of the thallus in process of division, X80; B, growing point of a branch showing the two-sided apical cell (x) and the ventral hairs (h), X240; C, the growing point in process of division, x, x', the apical cells of the two branches, X480. the same, and is effected by the growth of a "two-sided" apical cell.^ The segmentation is very regular, especially in Met/:geria (Fig. 37), where each of the segments divides first into an inner and an outer cell, the former by subsequent divi- sions parallel to the surface of the thallus producing the thick- - . '■ • ' ' ^Leitgeb (7), vol. iv. 86 MOSSES AND FERNS CHAP. ened midrib, the outer cells dividing only by perpendicular walls, forming the wings. From the ventral surface of the young midrib papillae project, which curve up over the grow- ing point, in the form of short two-celled hairs, whose end cells secrete mucilage for its protection. In Aneura the growth is very similar, but all of the cells divide by walls parallel to the surface of the thallus, and no midrib is formed, and the thallus is several cells thick in all parts. In both genera numer- ous delicate colourless rhizoids are developed from the ven- tral surface, especially of the midrib, when that is present. Aneura is of interest as showing the only case among the Bryophytes of structures that may be compared to the zoo- A. Fig. 38. — A, Symphyogyna sp.; B, Hymenophyton Habellatum, XiJ^; sp., young sporophyte; b, young shoot. Spores of the Green Algae. In A. multifida Goebel ((8), p. 337), discovered that the two-celled gemmae which had been described as formed simply by a separation of the cells of the thallus, were really formed within the cells and expelled from them through an opening, after which they divided into two cells and ultimately developed a young plant, much as an ordi- nary spore would do. The absence of cilia from these cells, which probably are the last reminiscences of the ciliated go- nidia of the aquatic ancestral forms, is to be accounted for by the terrestrial habit of Aneura. The branching is dichotomous, and is brought about by Ill THE JUNGERMANNIALES 87 the formation of a second apical cell in one of the youngest segments. This apical cell is formed by a curved wall, which strikes the outer wall of the segment ( iMg. 37, C). Thus two apical cells arise close together, and as segments are cut off from each, they are forced farther and farther apart, and serve as the growing point of two shoots, which may continue A Fig. 39. — Aneura pinnatiUda. A, Part of a thallus with two antheridial branches, slightly magnified; B, an archegonial branch, X40; C, cells from the margin of the archegonial branch showing the oil bodies (0), X300. to grow equally, when the thallus shows a marked forking (M. furcata), or one of the branches grows more strongly than the other, which is thus forced to one side and appears like a lateral branch {Aneura pinnatiiida, Fig. 41, B). In certain species of Pallavicinia and Symphyogyna, and especially in Hymenophyton (Fig. 38, B), the gametophyte shows a differentiation into a prostrate rhizome-like sterj, 88 MOSSES AND FERNS CHAP. from which arise upright flattened shoots which are repeatedly forked, so that there is a remarkably close superficial resem- blance to the fan-shaped leaves of certain Ferns, especially some of the smaller Hymenophyllacese. This resemblance is heightened by the very distinct midrib traversing each thallus- segment. Sexual Organs. The sexual organs in both Aneura and Met2geria are borne on short branches, which in the latter arise as ventral struc- FiG. 40.'-^Aneura pinnatiUda. A, Horizontal section of the apex of a young antheridial branch, X565; x, the apical cell; (^, antheridia: B, transverse section of a young archegonial branch, passing through the apical cell (x) ; J, young archegonia, X525; C, longitudinal section of a nearly ripe archegonium, X262; D, E, spermatozoids of Pellia calycina, X1225 (D, E, after Guignard). tures, but in Aneura are simply ordinary branches that are checked in their growth by the production of the sexual or- gans, and not infrequently may grow out into ordinary branches after the formation of the sexual organs has ceased. In A. pinnatifida (Fig. 39, B), archegonia and antheridia are usually produced upon separate branches, but may occur to- gether. The origin of the antheridia can be readily followed in Ill THE JUNGERMANNIALES 89 sections made parallel to the surface of the male branch. The apex is occupied by an apical cell of the usual form, and the cell divisions in the young segment arc extremely regular. The segment first divides into an inner and an (jutcr cell, and the former probably next into a dorsal and a ventral fjne. The dorsal cell divides by a longitudinal wall into t\v(j nearly equal cells, of which the inner one, dividing by a wall perpendicular to the first, gives rise to the primary cell of the antheridium (Fig. 40, Ac^). This cell now projects above the surface of the thallus, and divides into a single stalk cell, which under- goes no further divisions, and the antheridium mrjther cell. The divisions in the latter correspond to those in the other Jungermanniales. First a vertical w^all is formed, dividing the young antheridium into two equal parts. Next, in each of these, two walls arise intersecting each other as well as- the median wall, and dividing each half of the antheridium into three cells, two peripheral ones and a central ofie. (A some- what later stage than this is shown in Fig. 40, A.) The per- ipheral cells do not reach to the top of the antheridium, and next a periclinal wall is formed near the top of the central cells, by which a third peripheral cell is formed in each half of the antheridium, which now consists of two central cells and six peripheral ones. The further divisions were not followed in detail, but seem to correspond with those in the higher forms. Of the two first cells into which the dorsal cell divides, the one which does not produce the antheridium together with the inner of the two into which that cell first divides, form a par- tition w^hich rapidly increase^ in height vvith the growth of the antheridia, and separates 'each from its neighbour by a single layer of cells, so that the antheridia are sunk in cham- bers, arranged in two rows, corresponding to the two series of segments of the apical cell. In the other thallose anacrogynous forms, c. g., Palla- vicinia (Fig. 41, A), the sexual organs are borne upon the dorsal surface of the ordinary shoots, usually surrounded by a sort of involucre. In most of these forms the apical cell is of a different type from that of Anciira, but is variable even in the same species. Thus in Pallavicinia cylindrica, while the commoner form is nearly wedge-shaped, appearing four- sided seen from the surface, and triangular in vertical section, it may approach very nearly the two-sided type (Fig. 42, C). 90 MOSSES AND FERNS CHAP. In the ordinary form four sets of segments are cut off, — dorsal and ventral, as in Riccia or Sphcerocarpus, and two sets of lateral ones. In Pellia calycina the apical cell shows a similar form, but in P. epiphylla (Fig. 42, D, E), another type is seen. Here, while the surface view is the same as in P. caly- B. A Fig. 41.— a, Pallavicinia cylindrica, X4; per, the elongated perianth; B, Aneura pin- natiUda, X6; J, archegonial branches; C-E, Fossombronia longiseta, X4; F, Blasia pusilla, X4. cinaj in vertical section the cell is nearly semicircular, i. e., here there are but three sets of segments, two lateral ones and a basal one, extending the whole depth of the thallus, and only m THE JUNGERMANNIALE^ 02 Fig. 42. — A, Vertical, B, C, horizontal sections through the apex of Pallavicinia cylindrica; x, apical cell, A, X225; B, C, X450; D, E, Pellia epiphylla; U, ver- tical section; E, horizontal (optical) section, X4S0. 92 MOSSES AND FERNS CHAP. later showing a division into ventral and dorsal cells. Prob- ably this type has been derived from the former by a gradual increase in the size of the angle formed by the dorsal and ven- tral walls of the apical cell, which finally became so great as to practically form one plane. The antheridium of Pellia is larger than that of Aneura, but its development is very similar except that the stalk is multicellular, as it is in the other Anacrogynse. The sperma^ tozoids of Pellia (Fig. 40, D, E), are much larger than those of Aneura, but are exceeded in size by those of the allied genus Makinoa (Miyake (2)). \ "\^ / / Fig. 4S.—Fossom'bronia longiseta; early stages in the development of the antheridium, X525; drawings made by Mr. H. B. Humphrey* D, cross-section. In Fossombronia (Fig. 43), which in several respects re- calls Sphcerocarpus or Geothallus, the first divisions in the an- theridium are median ones, so that in both longitudinal and transverse sections the antheridium appears to be divided into equal quadrants. The first division, however, is vertical, as it is in Aneura. The archegonia are borne upon similar but shorter branches and their development also is very regular. In Fig. 40, B, a vertical section through the end of a young female branch is shown with the apical cell {x). Segments are here, too, cut Ill THE JUNGERMANNIALES 93 off alternately right and left, and from each segment an arche- gonium develops. The segment is first divided, probahly, as in the male branch and the vegetative ones, into an inner and an outer cell, but I did not succeed in getting satisfactory longi- tudinal sections parallel to the surface, so cannot speak posi- tively on this point. The youngest segment, in which the archegonium mother cell is recognisable, shows in vertical sec- tion three cells, a small ventral one, a middle larger one, anrl a dorsal one — the archegonium mother cell. The latter does not form any stalk, but divides at once by the three intersect- ing walls, as in other Hepatic?e, and the further development corresponds with these, except that the base of the archegonium B. Fig. 44. — Fossomhronia longiscta. Development of the archegonium, longitudinal sec- tion, XS25; drawings made by Mr. H. B. Humphrey. is not free, and the central cell is below the level of the super- ficial cells of the thallus. The archegonium neck is short, and the basal part as w^ell as that part of the venter which is free, two cells thick (Fig. 40, C). The number of neck cells Is small (apparently about four), but whether the number is con- stant cannot be stated positively. The female branch remains 94 MOSSES AND FERNS chap. very short, and the archegonia, which are only produced in small numbers (usually not more than six to eight), are close together and surrounded by an irregular sort of envelope formed by the more or less incurved and very much laciniated margins of the branch. Secondary hair-like growths are also formed, so that to the naked eye the archegonial receptacles appear as densely fringed and flattened tufts upon the sides of the larger branches. The archegonium of Fossombronia (Fig. 44) closely re- sembles that of Sphcerocarpus, but it ordinarily has but five peripheral rows of neck-cells, as in most of the Jungerman- niales. Occasionally, however, there may be six rows, as in Sphcerocarpus. Janczewski ( i ) followed very carefully the development of the archegonium in Pellia epiphylla, which differs a good deal from that of Aneura. The archegonia are formed in groups just back of the apex, but he does not seem to have been able to detect any relation between them and the segments of the apical cell such as obtains in Aneura, but it seems probable that such a relation does exist. After the archegonium mother cell is cut off, it does not at once divide by vertical walls, but there is first cut off a pedicel, after which the upper cell under- goes the usual divisions. Of the three peripheral cells one is much smaller and does not as a rule divide longitudinally, so that the neck has normally but five rows of cells instead of six, as in the Marchantiacese. Owing to the formation of the pedicel, the archegonium is quite free at the base, and like that of Aneura the wall of the venter is two-layered. The neck becomes very long, and, according to Janczewski, the number of neck canal cells may reach sixteen or even eighteen. The Sporophyte The earliest stages in the embryo are not perfectly known. Kienitz-Gerloff (i) investigated Metzgeria furcata and Leit- geb ((7), III) species of Aneura. In both of these the first division in the embryo separates an upper cell, from which capsule and seta develop, from a lower cell, which forms a more or less conspicuous appendage at the base of the foot. The earliest divisions in the upper part are not known, but it soon becomes a cylindrical body consisting of several tier3 of in THE JUNGERMANNIALES 95 cells, each composed of four equal quadrant cells. According to Leitgeb (i), the upper tier, from which the capsule develops, is formed by the first transverse wall in the up])er part of the embryo. This upper tier is next divided by nearly transverse walls into four terminal cover cells, and four larger ones below, and these latter are again divided each into three cells, an inner one and two outer ones, so that the capsule consists of four central cells, the archesporium, and twelve wall cells (Fig. 45, A). A similar division in the lower tiers results in the forma- tion of four axial rows and a single outside layer of cells in the stalk. In the lowest tiers the divisions are much less regu- lar, and the foot, which is not very largely developed, shows A Fig. 45.^A, Young embryo of Aneura midtifida, optical section, X235 (after Leit- geb); B, median longitudinal section of an older sporogonium of A. pingnis, X35\ C, upper part of B, X200; sp, sporogenous cells; el, young elater,s; m, apical group of sterile cells. no definite arrangement of the cells. The part of the wall of the capsule formed from the four cover cells later become two- layered, but the rest remains but one cell thick. In Metzgcria (Leitgeb (7), III.) the wall becomes later two-layered. The archesporium divides first into two layers. In the upper cells the divisions are more regular than in the lower one, and later the archesporium is made up of cells arranged in more or less regular lines, starting from just below the apex and radiating from this point, extending to the base of the capsule. These cells are at first of similar form, and with 96 MOSSES AND FERNS CHAP. the growth of the capsule become elongated with pointed ends that fit together without any spaces between. Some of these cells, however, divide rapidly by transverse walls and give rise to rows of isodiametric cells (Fig. 45, sp), wedged in between others that have remained undivided (el). The former are the young A . sporogenous cells, the latter the elaters. A mass of cells lying just below the apex, and belonging to the archesporium, re- mains but little changed, and forms the point of attachment for the elaters after the capsule opens (Fig. 45, B, C, m). See also Goebel ((21), pp. 325-327. The further develop- ment of spores and ela- ters is similar to that in the higher Marchantia- cese, and when the cap- sule is mature it opens by four valves which extend its whole length. '- -^ The first division-wall in the embryo of Fos- sombronia longiseta is transverse and divides it into two somewhat un- equal cells, of which the Fig 46.-Fossombronia longiseta. A Section j^^^^^ ^^^ Smaller One through a young tetrad of spores; B, surface view of the wall of a young spore; C, two givCS risC tO the foOt, and young elaters, X6oo; D. two ripe spores; E, ^^^ merely tO the append- elaters, X300. -^ ^y age of the foot, as is the case in Aneiira. From the upper cell arise the seta and the capsule. A second transverse wall (Fig. 47, 11.) is formed before any longitudinal walls appear. The upper of the three cells gives rise, not only to the capsule, but to part of the seta as well. The separation of the primary archesporial cells is m THE JUNGERMANNIALES 97 brought about by a periclinal wall in each of the four terminal cells, dividing each into an inner archesporial cell, and an outer wall-cell. (Fig. 47, D.) The capsule wall in Fossomhronia is two cells in thickness, except at the apex, where it may be three cells thick. The inner layer of cells, when the capsule is ripe, have irregular thickened bars developed upon the surface of the radial cell- walls. The development of the sporogonium is best known in Pellia epiphylla (Kienitz-Gerloff (i), Hofmeister (i) ). Here the first wall, as in Aneura, separates a lower cell, which sim- ply forms an appendage, from the upper cell, from which the B. Fig. 47. — Fossomhronia longiseta. Development of the embryo, X525; B, E, cross- sections; D, shows one of the primary archesporial cells. Figures drawn by Mr. H. B. Humphrey. stalk and capsule develop. In the latter the first wall is ver- tical, and is followed in each of the resulting cells by horizontal walls, by which the separation of the capsule from the seta is effected. These four cells are now divided by vertical walls, so that two layers of four cells each are present. The first periclinal walls in the apical group of cells separate the arch- esporium from the wall of the capsule. 98 MOSSES AND FERNS chap. The differentiation of the capsule and seta follows as in 'Aneura, and the arrangement of the cells of the archesporium is much the same except that the rows of cells radiate from the base of the capsule and not from the summit. The foot is very distinct and forms a pointed conical cap, whose edges overlap the base of the seta. Spore-division in Anacrogynce According to Farmer (4), in Pallavicinia decipiens there is formed, previous to the division of the nucleus, a "quadripolar" nuclear spindle, extending into each of the four lobes of the spore mother-cell. Then follows a double division of the chromosomes, resulting in sixteen, of which four move to each pole of the spindle to form at once the four nuclei of the spore tetrad. In Aneura multiUda the formation of a quadripolar spindle was also found, but there were subsequently two suc- cessive nuclear divisions of the usual type. From his study of Pellia epiphylla, Davis (3) has questioned the accuracy of Farmer's statements, and Moore's ( i ) studies on Pallavicinia Lyalii show that in this species, although a structure which might be interpreted as a quadripolar spindle is present, there are two successive divisions of the nucleus with bi-polar spin- dles. However, the second mitosis follows without an inter- vening resting stage of the nucleus. The growth of the seta after the spores are ripe is ex- tremely rapid, but consists entirely in a simple elongation of the cells. Askenasi ( i ) has investigated this in Pellia epi- phylla, and states that in three to four days the seta increases in length from about i mm. to in some cases as much as 80 mm., and that this extraordinary extension is at the expense of the starch which the outer cells of the young seta contain in great abundance, but which disappears completely during the elongation of the seta. The growing sporogonium here as well as in other species is strongly heliotropic. The calyptra in the thallose Anacrogynse is usually massive, and in addition there is formed about the growing sporogo- nium a special envelope inside the involucre, which in Palla- vicinia especially (Fig. 41, A) becomes prolonged into a tube which completely encloses the sporogonium until just before its dehiscence. Ill THE JUNGERMANNIALES 99 The further development of the spores and elaters corre- sponds with that of the Marchantiacea^ (Fig"- 4^), and there is the same method of the development of the thicken- ings upon the walls of the elaters and the spores. In cases where the spores germinate immediately, chlorophyll is devel- oped and no proper exospore is formed, although the outer layer of the cell wall is more or less cuticularised. In the germination of the spores Pcllia offers an exception to the other Jungermanniales, in that the spores divide into a multicellular body before they are discharged from the cap- sule. The presence of centrospheres in the dividing nuclei has been demonstrated by Farmer ( 5 ) , and recently Chamber- lain (2) has studied these bodies very thoroughly in Pellia. The ripe spore here is an oval body which consists of several tiers of cells, the end cells being usually undivided, and the middle ones each consisting of four equal quadrant cells. There is some disagreement as to the earliest stages in the germination and the establishment of the apical growth. Hof- meister ((i), p. 21) states that in F. epiphylla one end cell of the spore grows out into the first rhizoid, while the other develops into the growing point of the young plant. Miiller, N. J. C. ( ( I ), p. 257), on the other hand, states that in P. caly- cina both ends of the spore develop rhizoids while the growing point, which at first has a two-sided apical cell, like that of Metzgcria, arises laterally. The germination of the spores of Aneiira has been studied by Kny ( i ) in A. palmata, and by Leitgeb ( (7), III., p. 48) in A. pingiiis, which agrees in all respects with the former. The spores, as is usual in the Jungermanniales, have a poorly-de- veloped exospore, and contain chlorophyll when ripe. Before any divisions take place, the spore enlarges to two or three times its original volume, and then elongates and by repeated cross-walls forms a filament of varying length. In the end cell next an inclined wall arises, w^hich is met by another nearly at right angles to it, and thus the two-sided apical cell is established, and the thallus gradually assumes its complete form (Fig. 48, A). Connecting the strictly thallose anacrogynous Hepaticas with the foliose acrogynous ones, are a number of most in- structive intermediate forms. Of these Blasia (Fig. 41, F) is perhaps the simplest. Here the margin of the thallus is lobed, 100 MOSSES AND FERNS CHAP. and these lobes, according to Leitgeb's view, are very simple leaves. In Fossombronia (Fig. 41, C, D), while the general thallose form is more or less evident, the leaves are unmistak- able, and as their development shows, morphologically the same as the leaves of the acrogynous forms. The most re- markable form, however, is Treubia insignis, a very large foliose Liverwort discovered by Goebel in Java. This has all the appearance of a very large acrogynous form, and also the typical three-sided apical cell; but in regard to the position of the sexual or- gans it is typically ana- crogynous. These and the Haplomitriese form a per- fect transition from the Anacrogynse to the Acro- gynse. The multicellular gem- mae of Blasia have been al- luded to. They are pro- duced in long flask-shaped receptacles, and when ma- ture forrn nearly globular brownish bodies whose cells contain much oil, and whose stalk consists of a simple row of cells. Among them are glandular hairs, which secrete mucilage, by the swelling of which the gemmae are loosened from their pedicels, as in Mar- chantia. Similar but sim- pler gemmae having usually three cells occur in Treubia (Goebel (13)). Blasia is also characterised by the presence of colonies of Nostoc within the thallus. These occupy cavi- ties in the bases of the leaves and are normally always present. The Haplomitriece The two genera, Haplomitrium and Calobryum, which con- B Fig. 48. — A, Young plant of Aneura palmata X265 (after Leitgeb) ; B, three views of a young plant of Pellia calycina, X420 (Leitgeb). m THE JUNGERMANNIALES loi stitute this family, differ from all other Ilepaticae in having the leaves radially arranged, and not showing the dorsi ventral form that characterises all the others. The i)lants are com- pletely destitute of rhizoids hut ])ossess a rhizcjme-like basal part, from which the leafy axes arise. The latter have well- developed leaves arranged more or less distinctly in three rows. The stem growls from a tetrahedral ai)ical cell, as in the acrog- ynous forms, but in Haploniitriinn at least the apical cell does not develop into an archegonium. The archegonia are in this genus borne at the end of ordinary shoots, but in Calobrynm the end of the female branch becomes much broadened and the numerous archegonia stand crowded together. In this case it is possible that the apical cell of the stem may finally produce an archegonium. Much the same difference is ob- servable in the arrangement of the antheridia. The Acrogyn^ Treuhia and Haplomitrium, as we have seen, connect al- most insensibly the anacrogynous with the acrogynous Jun- germanniales. The latter are much more numerous than the former, but much more constant in form, and are doubtless a later specialized group derived from the former. While dif- fering in the form and arrangement of the leaves and other minor details, they are remarkably constant in their method of growth and in the position of the sexual organs, especially the archegonia. These are always formed upon special branches, where, after a varying number of segments are cut off, the apical cell becomes the mother cell of an archegonium. The study of any typical form w^ill illustrate the principal characters of the group. The species selected, Porella {Ma- dotheca) Bolanderi, is very like the common and widely dis- tributed P. platyphylla, which corresponds with it in all struct- ural points. The plant grows upon rocks, especially, but also upon the trunks of trees, and forms dense mats closely covering the substratum. It branches extensively, but always monopodi- ally, dichotomous branching never occurring in the acrogynous Jungermanniales. The slender stem is completely hidden above by the two row^s of closely-set, overlapping, dorsal leaves. Upon the ventral side, which is fastened by scattering 102 MOSSES AND FERNS CHAP. rhizoids to* the substratum, there is a row of much smaller leaves (amphigastria), more or less irregularly disposed. The dorsal leaves, seen from above, are nearly oval in outline, but each has a smaller ventral lobe, pointed at the tip, and closely appressed to the lower surface of the much larger dorsal lobe. The ventral lobes closely resemble the amphigastria, both in form and size, and with the latter form apparently three rows of leaves upon the ventral side of the stem. The structure of the leaf is of the simplest character, consisting of a single layer of polygonal cells containing numerous chloroplasts. The plants grow where they are exposed to alternate wetting and drying up. They may at any stage become com- pletely dried up, and on being moistened will re- sume at once their ac- tivity. In the dried con- dition, the species under consideration often re- mains for several months without appa- rently being injured in the least, and this power is shared to a consider- FiG. 49.— Porella Bolanderi. A, Female plant, X4; ^^ablc degree by mOSt of 5, archegonial branches; E, an open sporogo- the aCrOgyUOUS formS, nium, X4; C, a male plant, X4; r?> the an- •• ,. ., 1 1 •, , theridiai branches. whosc favourite habitat is the trunks of trees. The apical growth of the stem is extremely regular, and as in ail the other acrogynous Hepaticse, the apical cell is a three- sided pyramid (Fig. 50, A). In longitudinal section it is much deeper than broad, and its outer face is almost flat. In cross-sections (Fig. 50, B) it has the form of an isosceles tri- angle, the shorter side turned toward the ventral surface of the plant. From this cell three sets of lateral segments are cut off, two dorsal and one ventral, and "each of these gives rise to a row of leaves, a leaf corresponding to each segment of the apical cell. The first division wall in each segment is at right ; angles to its broad faces and divides it into two cells of some- .s. Ill THE JUNGERMANNIALES 103 what unequal size. The next wall formed divides the larger of the two primary cells into an inner and an outer cell (Fig. 50, A), so that the young segment now consists of three cells, an inner one and two outer ; the latter in the dorsal segments correspond to the two lobes usually found in the dorsal leaves. The two outer cells now divide by walls in two planes, and rapidly grow out above the level of the apical cell and form Fig. so. — Porella Bolanderi. A, Median longitudinal section of a vegetative axis; B, a cross-section of the apex of a similar one, X500; x, the apical cell; h, hair; d, dorsal surface; v, ventral surface; C, male; D, female branch. lamellae which remain single-layered, and undergo but little further modification beyond an increase in size. From the base of the young leaves simple hairs develop, but remain small and inconspicuous. The inner of the three first formed cells of the segment, by further division and grow^th in all direc- tions, produces the axis of the plant. This in cross or longi- tudinal section shows almost perfectly uniform tissue. No distinct epidermis, or central strand, like that found in most Mosses, can be seen. I04 MOSSES AND FERNS chap; The branching is monopodial and the branch represents the ventral lobe of a leaf. After the first division by which the two lobes of the leaf are separated, only the dorsal one develops into the lamina of the leaf, which is thus in the seg- ment from which a branch is to form, only one-lobed. In the ventral cell three walls arise (Fig. 51), intersecting so as to cut out a pyramidal cell of the same form as the apical cell of the main axis, and the cell so formed at once begins to divide y. Fig. 51. — Diagram showing the ordinary method of branching in the acrogynous Jun- germanniaceae (after Leitgeb). D, Dorsal; V, ventral side of stem; X' X", apical cells of the branches. The segments are numbered. in the same way, and forms a lateral axis of precisely the same structure as the main one. The genus Physiotium differs from all other known Acrog- ynse in having a two-sided apical cell, instead of the typical tetrahedral one — (Goebel (21), p. 287). The Sex-organs The plants in Porella are strictly dioecious and the two sexes are at once recognisable. The males are smaller, and bear special lateral branches which project nearly at right angles from the main axis, and whose closely imbricated light green in THE JUNGERMANNIALES 105 leavei. make them conspicuous. At the base of each of the leaves is a long-stalked antheridium, large enough to be readily seen with the naked eye. The development of the antheridium may be easily traced by means of sections made parallel to the surface of the branch. At the apex (Fig 50, C) is an apical cell much like that in the sterile branches, but with the outer face more convex. The divisions in the segments are the same as there, but the whole branch remains more slender, and the hairs at the base of the leaves are absent. The antheridia arise singly from the bases Fig. 52.— P CO 3 -J o'i .. 3 .2 3 c ^ o bed che lise U '.^ rt t: ^'H c 3 u O J5 ►. •- « ^ • * <-• '"^ -S Of rt "^ ti c rt O — y C as O 3 « 5 u p U O O o > « . J3 < " ■«"■ o o s ■« s .- X ium c 5 = *•«-» 2^ CO 2 « ^ o. 3 S 'u ■4-* 1 >> Si a 1 -z ^ c o M P^ 128 MOSSES AND FERNS chap. Each cell of the thallus contains a single chloroplast which may be either globular or spindle-shaped, or more or less flattened. The nucleus of the cell lies in close contact with the chloroplast, and usually partly or completely surrounded by it. There is no separation of the tissues into assimilative and chlorophylless, as in the Marchantiacese, and in this respect Anthoceros approaches the simplest Jungermanniacese, as it does in the complete absence of ventral scales or appendages of any kind, except the rhizoids. The infection of the plant with the Nostoc has been care- fully studied by Janczewski and Leitgeb ((7), v., p. 15). The infection takes place while the plant is young, and is usually brought about by a free active filament of Nostoc making its way into the intercellular space below the mucilage slit, through whose opening it creeps. Once established, the filament quickly multiplies until it forms a globular colony. The presence of the parasite causes an increased growth in the cells about the cavity in which it lies, and these cells grow out into tubular filaments which ramify through the mass of filaments, and becomes so interwoven and grown together that sections through the mass present the appearance of a loose par- enchyma, with the Nostoc filaments occupying the interstices. Other organisms, especially diatoms and Oscillarece, often make their way into the slime cavities, but according to Leit- geb's investigations their presence has no effect upon the growth of the thallus. Sexual Organs. The plants are monoecious in A. fusiformis, and this is true of other species observed. In the former, however, the antheridia appear a good deal earlier than the archegonia. I observed them first on young plants grown from the spores, that were not more than 3 mm. in length. The exact origin of the cell which the antheridia develops could not be made out, as none of my sections showed the youngest stages. Waldner's (2) observations upon A. Icevis, however, and my own on A. Pearsoni and Notothylas valvata, as well as a study of the older stages in A. fusiformis, leave no doubt that in this species as in the others the antheridia are endogenous, and the whole group of them can be traced back to a single cell. They arise close to the growing point, and the cell from which they IV. THE ANTHOCEROTES i2g arise is the inner of two cells formed by a transverse wall in a surface cell. The outer cell (see Figure 67, 1>) divides almost immediately by another wall parallel with the lirst, S(j that the group of antheridia is separated by two layers of cells from the surface of the thallus. The inner cell in A. Pcarsoni at once develops into an antheridium ; but in most species the cell divides first by a longitudinal wall into two, each of which Fig. 67. — Anthoceros Pearsoni. Development of the antheridium: A, apex of the thallus, with very young antheridium, X about 500; B, a somewliat older stage; C, still older stage, somewhat less highly magnified; D, an older, but still im- mature antheridium, X about 200. generally divides again, so that there are four antheridium mother cells, all, how^ever, unmistakably the product of a single cell, and if a comparison is to be made with the antheridium of any other Liverwort, the antheridium in the latter is homol- ogous, not with the single one of Anthoceros, but with the whole group, plus the two-layered upper wall of the cavity in which they lie. The first divisions in the antheridium are the same as those in the original cell, i.e., the young antheridium is divided longi- tudinally by two intersecting walls, and the separation of the 9 I30 MOSSES AND FERNS CHAP. stalk from the upper part is secondary; indeed in the earhest stages it is difficult to tell whether these longitudinal divisions will result in four vSeparate antheridia or are the first division walls in a single one. Secondary antheridia arise later by budding from the base of the older ones, so that in the more advanced conditions the antheridial group consists of a varying number, in very different stages of development (Fig. 68, A). A /->^.--<^>N C, I D Fig. 68. — Anthoceros fusiformis. Development of the antheridium ; D, E, drawn from living specimens, the others microtome sections; D, i, shows the single chloroplast in each of the wall cells, and the secondary antheridium {s) budding out from its base; 2 is an optical section of the same; E, surface view of full-grown antherid- ium; F, cross-section of a younger one. Figs. A, E X225, the others X4S0. After the first transverse walls by which the stalk is separated, the next division in each of the upper cells is parallel to it, so that the body of the antheridium is composed of nearly equal octant cells. Then by a periclinal wall each of these eight cells is divided into an inner and an outer cell, and the eight central ones then give rise to the sperm cells, and the outer ones to the wall. The four stalk cells by repeated transverse divisions form the four-rowed stalk found in the ripe antheridium. The uppermost tier of the stalk has its cells also divided by vertical walls and forms the basal part of the antheridium wall. The transverse and vertical division walls in the central cells alter- nate with great regularity, so that there is little displacement of the cells, and up to the time of the separation of the sperm IV. THE ANTHOCEROTES 131 cells the four primary divisions are still plainly discernible, and the individual sperm cells are cubical in form. In the per- ipheral cells hardly less regularity is observable. Except near the apex none but radial walls are formed after the first trans- verse v^all has divided the body of the antheridium into two tiers, and when complete the wall consists of three well- marked transverse rows of cells, the lower being derived from the uppermost tier of stalk cells. At the apex the cells are not quite so regular (Figs. D, E). In its younger stages the antheridium is very transparent and perfectly colourless. In each peripheral cell a chloroplast is evident, but at this stage it is quite colourless and the nucleus is very easily seen in close contact w^ith it. As the antheridium grows the chloroplasts develop with it, becoming much larger and elongated in shape, and at the same time develop chlorophyll. The mature chloro- plast is a flattened plate that nearly covers one side of the cell, and its colour has changed from green to a bright orange as in the antheridium of many Mosses. The sperm cells are dis- charged through an opening formed by the separation of the apical cells of the antheridium. These cells do not become detached, but return to their original position, so that the empty antheridium has its wall apparently intact. The sperma- tozoids are small and entirely like those of the other Hepaticse. Leitgeb ((7), v., p. 19) found in abnormal cases that the antheridia may arise superficially, as in the typical Hepaticse. Lampa ( i ) describes a similar exogenous origin for the antheridium, but Howe (5) has questioned the accuracy of her statements, and thinks that the supposed antheridia were tubers, as Frau Lampa's figures do not agree with the structure of the typical antheridium. Whether this exogenous developn ment of the antheridium is a reversion to a primitive condition is impossible to decide, but it is possible that such is the case. At first the cell from which the antheridial complex arises is not separated from its neighbours by any space. About the time that the first divisions in it are formed, the young antheridial cells begin to round off and separate from the cells above them. With the growth of the surrounding cells this is increased, so that before the divisions in the separate cells begin, the group of papillate cells is surrounded by a cavity of considerable size. To judge by the readiness with which the walls of the cavity stain, it is probable that the 132 MOSSES AND FERNS chap. separation of the cells is accompanied by a mucilaginous change in their outer layers. The first account of the archegonium was given by Hof- meister, who, however, overlooked the peripheral cells and only saw the axial row. Later Janczewski (2) showed that Antho- ceros did not differ essentially in the development of the archegonium from the other Hepaticae, and his observations were confirmed by the later researches of Leitgeb and Wald- ner (2). The formation of archegonia does not begin until the older antheridia are mature, and very often, especially in A. Pearsoni, few or no antheridia were found on the plants with well-developed archegonia. After the formation begins, each dorsal segment gives rise to an archegonium, so that they are arranged in quite regular rows, in acropetal order. After the transverse wall by which the segment is divided into an inner and an outer cell is formed, the outer cell becomes at once the mother cell of the archegonium, much as in Aneura. In this cell next arise three vertical intersecting walls, by which a triangular (in cross-section) cell is cut out as in the other Hepaticse. Sometimes it looks as if one of these walls was suppressed, but even in such cases the triangular form of the central cell is evident. The main difference between the archegonium at this stage in Anthoceros and the Hepaticse lies in the complete submersion of the archegonium rudiment in the former. In this respect Aneura, where the base of the archegonium is confluent with the cells of the thallus, offers an interesting transition between the other Hepaticae, where the base of the archegonium is entirely free, and Anthoceros. The archegonium rudiment divides into two tiers as in the other Liverworts, and the peripheral cells divide longitudinally, and the neck shows the six vertical peripheral rows although it is completely sunk. Later, the limits of the neck become often hard to determine, although by later divisions the central cell is surrounded by a pretty definite layer of cells. The axial cell divides into two of nearly equal size, but the inner one soon increases in breadth more than the upper one. The latter divides again by a transverse wall into an outer cell corre- sponding to the cover cell of the ordinary hepatic archegonium, the other to the primary neck canal cell. The cells of this cen- tral row soon become clearly different from the other through their more granular contents. The lower cell grows much IV. THE ANTHOCEROTES 133 faster than the others and divides into the Qgg cell and the ventral canal cell. The cover cell divides by a vertical wall into two nearly equal cells, and these usually, but not always, divide again, so that four cells arranged cross-wise form the apex of the archegonium. In A. fusiformis in nearly ripe archegonia I have sometimes been able to see but two of these cover cells, but ordinarily four are present. The neck canal cell divides first into two, and these then divide again, so that four cells are formed. This was the ordinary number in A. fusiformis. In a nearly ripe archegonium of A. Pearsoni five neck canal cells were seen, but in no cases so many as B. C. Fig. 69. — Anthoceros fusiformis. A two-celled embryo within the archegonium venter, X600; B, C, two longitudinal sections of a four-celled embryo, X600. Janczewski describes for A. Icevis, where he says as many as twelve may be present. If the earlier divisions in the archegonium of Anthoceros are compared with those of the other Hepatic^e, the most strik- ing difference noticed is the separation of the cover cell. In the latter the first division of the axial cell separates the cover cell from an inner one, and by the division of the latter the primary neck canal cell is cut off from the central cell. In Anthoceros the neck canal cell is cut off from the outer, and not from the inner cell. 134 MOSSES AND FERNS chap. As the archegonium approaches maturity the cover cells become very much distended and project strongly above the surrounding cells. In stained microtome sections their walls colour very strongly, showing that they have become partially mucilaginous. This causes them to separate readily, and they are finally thrown off, so that in the open archegonium no trace of them is to be seen. The walls of the canal cells and the central cell undergo the same mucilaginous change, but here it is complete, and before the archegonium opens the partition walls of the canal cells completely disappear, and the neck con- tains a row of isolated granular masses corresponding in num- ber to the canal cells. The ventral canal cell is quite as large as the egg, which consequently does not nearly fill the cavity at the base of the open archegonium (Fig. 66, D) after the canal cells have been expelled. The egg did not, in any sections studied, show clearly a definite receptive spot, but appeared to consist of uniformly granular cytoplasm with a nucleus of moderate size. The upper neck cells in the open archegonium become a good deal distended, and the canal leading to the egg is unusually wide. Surrounding the central cavity the cells are arranged in a pretty definite layer. Miss Lyon ((2), p. 288) states that she has frequently found archegonia in A. Icevis, produced upon the ventral side of the thallus. The Sporophyte Hofmeister was the first to study the development of the embryo in Anthoceros, and described and figured correctly the first divisions, but his account of the apical growth, which he supposed was due to a single apical cell, and the differentiation of the archesporium, was shown by the careful investigation of Leitgeb ((7), v.) to be erroneous. The following account is based upon a large series of preparations of A. Pearsoni and A. fusiformis, which seem to agree in all respects. After fecundation the egg at once develops a cellulose wall and be- gins to grow until it completely fills the centre cavity of the; archegonium. As it grows the uniformly granular appear^, ance of the cytoplasm disappears, and large vacuoles a're. formed, so that the whole cell appears much more transparent. The granular cytoplasm is now mainly aggregated about the nucleus, which has also increased in size (Fig. 66, E). The IV. THE ANTHOCEROTES I3S first division wall is parallel with the axis of the archegonium and divides the embryo into two equal parts, in which the character of the cells remains much as in the undivided tgg. Here too the granules are most abundant about the nucleus, from which radiate plates that separate the vacuoles. The next divisions are transverse and divide the embryo into two upper large cells and two lower smaller ones. The embryo at this stage is oval and more or less pointed above. In each of the four primary cells vertical walls arise that divide the embryo into octants, but the upper octants are decidedly larger than the lower. Next, in the upper cells, transverse w^alls are formed and the embryo then consists of three tiers of four cells each. Of these the cells of the upper tier are decidedly the larger. At this stage, in neither species examined by me, were any traces present of the projection of the basal cells figured by Leitgeb (1. c. PL L). As his drawings w^ere made from embryos that had been freed from the thallus, probably with the aid of caustic potash, it is quite possible that this ap- pearance was due in part at least to the swelling of the cell walls through the action of the potash. At any rate in micro- tome sections of both species in these early stages, the basal cells do not project in the least (Fig. 70, A). The next di- visions are very uniform in the upper tier of cells, from which the capsule develops, but less so for the two lower ones. In the upper tier, seen in cross-section (Fig. 70, B i), a slightly curved wall running from the median wall to the periphery forms in each quadrant, which thus viewed is divided into an inner four-sided and outer three-sided cell. In the former a periclinal wall next forms, w^hich cuts off an inner square cell (Fig. 70, D). In longitudinal section these periclinal walls are seen to be concentric with the outer walls of the cells, and to strike the median and quadrant w^alls at some distance below the apex of the sporogonium so as to completely enclose the central cells (Fig. 70, C). By the formation of these first periclinal w^alls the separation of the columella from the wall of the capsule is completed, and this is not unlike w-hat obtains in the sporogonium of many other Hepaticse; but an essential difference must be observed. In the latter the central group of cells forms the archesporium ; here these cells, as we shall see, take no part in spore formation. In the lower tiers of cells similar but less regular divisions occur (Fig. 70, D 2), 136 MOSSES AND FERNS CHAP. and the outer cells begin to grow out into root-like processes which push down among the cells of the thallus and obviously serve the purposes of haustoria. Leitgeb states that the foot arises only from the lowest of the primary tiers of cells, but in most of my sections of the earlier stages the fact that the foot was composed of two distinct layers of cells, corresponding in position to the two lower tiers of cells in the embryo, was very obvious (Fig. 70, E). Fig. 70. — Anthoceros Pearsoni. Development of the embryo X300; A, C, E, median longitudinal sections; B and D, successive cross-sections of embryos of about the age of A and C respectively. In E the archesporium is differentiated. The origin of the archesporium in Anthoceros was in the main correctly shown by Leitgeb, but I find that the extent of' the archesporium is less than he represents. In PI. I. Figs. 3 and 10 of his monograph on the Anthocerotese, he figures the archesporium as extending completely to the base of the columella. A large number of sections were examined, and in no case was this found to be so. Instead, it was only from' the cells surrounding the upper half of the columella that the archesporium was formed. Previous to the differentiation of) IV. . THE ANTHOCEROTES i37 the archesporium the four primary cells of the columella divide by a series of transverse walls until there are about four cells in each row. Radial walls also form in the outer cells so that their number also increases, and the young capsule consists of the central columella composed of four rows of cells and a single layer of cells outside. The archesporium now arises by a series of periclinal walls in the peripheral cells of the upper half only of the capsule, and is thus seen to arise from the peripheral cells of the capsule, and not from the central ones. Fig. 70, E shows a longitudinal section of the sporogonium at this stage. Three parts may be distinguished — the foot, the capsule, and an intermediate zone between. The latter is important, as it is from this that the meristematic part of the older sporogonium is formed. With the separation of the archesporium the apical growth ceases, and the future growth is intercalary. In the capsule cell divisions proceed rapidly in all its parts. The original four rows of cells forming the columella increase to sixteen, which is the normal number in the fully-developed sporogonium. The archesporium, by the formation of a sec- ond series of periclinal walls, becomes two-layered, and the wall outside the archesporium becomes about four cells thick, the outermost layer forming a distinct and well-developed epidermis. The foot grows rapidly in size, but the divisions are very irregular, and finally it forms a large bulbous appendage to the base of the sporogonium. The cells are large and the outer ones develop still further the root-like character of those in the young foot. The tissues of the thallus about the base of the sporogonium grow rapidly with it, and the connection between the surface cells of the sporogonium foot and the adjacent cells of the thallus is very intimate. The subsequent growth of the capsule is entirely dependent upon the activity of the zone of meristem at its base. This divides very actively, and the divisions correspond exactly with the primary ones in the young embryo, so that the completed portions of the older parts of the capsule are continuous with the forming tissues at the base. A series of cross-sections at different points, compared with a median longitudinal section, shows in a most instructive way the gradual development of the different parts of the mature capsule (Fig. y2). The centre 138 MOSSES AND FERNS CHAP. K of the sporogonium is occupied by a columella composed of sixteen rows of cells, which in cross-section form a nearly per- fect square. At the base these cells are thin-walled and show no intercellular spaces, but farther up their walls begin to thicken and the rows gradually separate until in the upper part the columella has somewhat the appearance of a bundle of isolated fibres. The archesporium is constantly growing from below, and the new cells are cut off from those surrounding the columella in the same way as at first. The archesporium, as well as the colu- mella, can be traced down nearly to the base of the capsule, and its cells are very early recognisable both by their position and by their contents. At first but one cell thick, the archesporium soon be- comes double, but does not advance be- yond this condition. As the archespo- rium is followed from the base towards the apex of the capsule the cells begin to show a differentiation. Up to the point where the archesporium becomes divided into two layers the cells appear alike; but shortly after this their walls begin to separate, and two distinct forms are recognisable, arranged with much regularity in many cases, although this arrangement is not invariable. Pretty regularly alternating are groups of oval, swollen cells, with large nuclei and abundant granular cytoplasm, and much more slender ones, that may un- dergo secondary longitudinal divisions. The latter have smaller nuclei and more transparent contents. Examination higher up shows that the former are the spore mother cells, the others the elaters, which here have the character of groups of cells, and do not develop the spiral thickenings found in most Hepaticse. As these two sorts of cells grow older they separate completely, and the spore mother cells become perfectly globular. The sterile cells remain more Fig. 71. — Anthoceros Pear- soni. Median longitudinal section through the base of the sporogonium. The archesporium is shaded. F, Foot; V, V, basal sheath of calyptra, Xioo. IV. THE ANTHOCEROTES I39 or less united, and form a sort of network in whose interstices the spores He. The development of the spores can be easily lollowed, at least in most of the details, in fresh material, and on this account it was among the first plants in which cell division was studied. The mother cells in all stages can be found in the same sporogonium, and on account of their great transparency show the process of cell division very satisfactorily. The nucleus, however, is small, and its behaviour during the cell division is not so easy to follow. The mother cell, just before division, is filled with colourless cell sap, and the cytoplasm is confined to a thin film lining the cell wall. This cytoplasmic layer is somewhat thicker on one side, and here the nucleus is situated (Fig. 73, A). Lying close to the nucleus is a round- ish body, of granular consistence and yellowish green in colour. This is a chloroplast, which at this stage is less deeply col- oured than later. The chloroplast contains a number of granules, some of which are starch. The cell increases rapidly in size, and the nucleus, together with the chloroplast, move away from the wall of the cell toward the centre, where they are suspended by cytoplasmic threads. The chloroplast next divides into two .equal portions, which move apart (Fig. 73, B), but remain connected by the cytoplasmic filaments. They approach again, and each dividing once more, the four result- ing chloroplasts remain close together with the nucleus, in the centre of the cell. Davis (i) has made a very complete study of the spore division in A. IcBvis. In this species the archesporium is less massive than in A. Pearsoni or A. fusiformis, and the ar- rangement of the sporogenous and sterile cells less regular. Davis found that the sporophytic nuclei had regularly eight chromosomes, those of the gametophyte four. Owing to the small amount of chromatin in the nucleus, the karyokinetic figures are small and the changes difficult to follow satisfactorily. Enough can be easily made out, how* ever, to show that the process is in no way peculiar. There is first a nuclear spindle of the ordinary form, and the resulting nuclei assume the resting stage before dividing again. Each then divides, and the four nuclei move to points equi- distant from each other, and which are already occupied by the four chloroplasts. After this is accomplished, cell walls arise IV. THE ANTIIOCEROTES 141 simultaneously between the four nuclei dividing the mother cell into four tetrahedral cells, — the young spores. The wall of the mother cell becomes thicker, and in the later stages swells up on being placed in water, so that it interferes a good deal wdth the study of the spores in the fresh condition. As the spores ripen they develop a thick exospore, which is yellow in colour and irregularly thickened in A. Pcarsoni, and in A. fiisiformis black and covered wnth small tubercles. The chlorophyll disap- pears and the spore becomes filled with oil and other food materials. The spores remain together until nearly ripe. The elaters, if this name can properly be applied to the sterile cells, at maturity consist of simple or branching B. "^• rows of cells, which in some cases arise from the division of a single one; but more com- monly, at least in A. Pcarsoni, where they branch, it is probable that they are to be looked upon as merely fragments of the more or less continuoiis net- work of sterile cells. The contents mainly disappear from the older elaters, and their walls become thick and in colour like the w^all of the spores. In A. fiisiformis they are longer and more symmetrical than in A. Icuvis, and in one group of the genus, according to Gottsche (2), the elaters, which consist of a row of five to six cells, have a distinct spiral band as in Dendroccros. Leitgeb thinks, however, that this group is more nearly related to the latter genus than to Anthoceros proper, inasmuch as in addition to the peculiar elaters the epidermis of the capsule has no stomata, w^hicli are always present in typical species of Anthoceros. If the epidermis from the young capsule is examined it is spen to be composed of elongated narrow cells much like those D Fig. 73. — Spore division in A. fusiformis; optical sections of living cells, X6oo. 142 MOSSES AND FERNS CHAP. in the epidermis of elongated leaves of Monocotyledons. In the older parts some of these cells cease to elongate, and be- come more nearly oval (Fig. 75, A). These are the young stomata, and exactly as in the vascular plants, each divides longitudinally by a septum which later separates in the middle and forms the pore surrounded by its two guard cells. The walls of the other epidermal cells become much thickened and distinctly striated. Each epidermal cell contains two large chloroplasts like that in the cells of the gametophyte, and be- tween the cells are well-developed air-chambers communicat- ing with the stomata, so that there is here a typical assimilative system of tissues. The doubling of the chloroplast in the cells of the sporophyte has been noted by Schimper (A. F. W. Schimper (2)), and Fig. 74. — Ripe spores and elaters of A. Pearsoni, X6oo. this was observed by the writer in both A. fusiformis and A, Pearsoni. About the base of the growing sporogonium is a thick tubular sheath representing in part the calyptra of the other Hepaticse, but involving, besides the archegonium venter, also the surrounding tissue of the gametophyte. This sheath keeps pace with the growth of the sporophyte for a long time, but finally the sporogonium grows more rapidly and projects far beyond it, and this remains as a tube surrounding its base. The growth of the sporogonium continues as long as the gametophyte remains alive, and in A. fusiformis is often 6 IV. THE ANTHOCEROTES 143 B centimetres or more in length, and reaches nearly this length before the first spores are ripe and the capsule opens. This it does by splitting at the top into two equal valves between which the dried-up columella protrudes. 11ie split deepens as the younger spores ripen, and may finally extend nearly to the base. It is quite possible, although this point was not investi- gated, that the line of dehiscence corresponds to the primary verti- cal wall in the embryo, as is the case in the Jungermanniacese. The germination of the spores^ has hitherto been ob- served only in A. IcBvis. A study of the germination in A. fiisi- formis shows a general corre- spondence with the results of other observers, but certain points were brought out that do not seem to have been observed in A. IcEvis. The spores of A. fusi- formis are protected by a per- fectly opaque black exospore, which is covered with small spines or tubercles. These spores will not germinate readily when fresh, but after resting for a few months grow freely. As in other similar spores, the ex- ospore is ruptured along the three ridges upon the ventral side {i. e., that with which it was in contact with the other spores of the tetrad), and through this cleft the endospore protrudes as a papilla which sometimes grows into a very long germ tube, or more commonly divides before it reaches a great length. Into this tube passes the single chromatophore which, during the early period of germination, has resumed its green colour, and with it the oil drops and other contents of the spore. A good deal of variation was observed here in the first divisions, as is the case in A. Icevis. The first division wall is, in most cases at least, transverse, and is usually followed by a second similar one, before any longitudinal walls appear. Then in the end cell two intersecting walls and the formation of four terminal quadrant cells are often seen (Fig. yS, D), as in other Hepaticae. Variations from this type are often met *Hofmeister (i) ; Gronland (i) ; Leitgeb (7), vol. v. p. 29. Fig. 7S.— a, Young ; B, fully developed stoma from the epidermis of the sporogonium oi A. Pearsoni, X250. 144 MOSSES AND FERNS CHAP. with, and some of these are shown in the figures. V^ery commonly a second cell is cut off by an oblique wall from the germ tube subsequent to the first transverse wall, but this does not, at least in the early stages, develop into a rhizoid, the first rhizoid being met with only after the young plant has become a cell body of considerable size (Fig. yy). Whether the young plant regularly grows from a single apical cell is difficult to say, but it seems probable, and numerous forms like Fig. 76, B were encountered where there certainly seemed to be a two-sided apical cell, such as occurs so often in Fig. 76. — Antlioceros fusiformis. Germination of the spores, X250. A shows a form with very long germ tube; in B there seems to be a definite apical cell; Fig. D, 2, is an apical view of D, i. Other Hepaticse. At a later stage (Fig. 77, B) a single apical cell of the form found in the mature thallus is unmistakably present. By this time the marginal lobes that give this species its peculiar crimped appearance begin to develop. They arise close to the growing point, and grow rapidly beyond it, but do not show any definite apical growth. The plant at this stage has a striking resemblance to the prothallium of Eqiiisetmn. With the appearance of the marginal lobes, the first of the mucilage slits appears upon the vental surface (Fig. yy), and from time to time surface cells grow out into the delicate IV. THE ANTHOCRROTES 145 rhizoids, and a little later the first dichotomy of the growing point takes place. Up to this time the young plants appeared entirely free from Nostoc, but soon after they were founrl to be infected, which no doubt was connected with the formation of the mucilage slits through which the Nostoc enters the thallus. In several species of Anthoccros, especially those inhabiting regions with a marked dry season, tubers are devcloj)ed by means of which the plants are perennial. Howe (3) finds such tubers developed in A. phymatodes, of California, and they are found in A. dichotomiis, of Southern Europe, and in A. tiihcr- sp Fig. 77.-^Anthoceros fusiformis. A, Young plant showing the first rhizoid (r) ; B, upper part of an older one with the first mucilage cleft (^0 ; x, the growing point, X215. osus of Australia (see also Goebel (22), p. 293). The struc- ture of these tubers has been studied by Ashworth (i), in A. tub er osus. Dendroceros Dendroceros includes about a dozen species of tropical Liv- erworts, which are distinguished at once from Anthoceros by the very characteristic form of the thallus. This has a massive midrib, projecting below^ but the rest of the thallus is but one cell thick and forms lateral wings which are much folded and lobed, so that the aspect of the plant is somewhat like a Fossoni- hronia. As in Anthoceros, some species have a perfectly com- 10 146 MOSSES AND FERNS chap. pact thallus without intercelluar spaces (D. cichoraceus) , while in others these are very much developed and the thallus has a more or less spongy texture, e. g., D. Javanicus. The develop- ment of the thallus and sporogonium has been studied by Leit- geb ( (7), v., p. 39), and in the main corresponds very closely to Anthoceros. A difference may be noted, however, in some details. Thus the form of the apical cell is like that of Pellia epiphylla, where the inner segments extend the whole depth of the thallus, and the division into dorsal and ventral seg- ments is secondary. The formation of the wings begins near the apex and is the result of the growth of the marginal cells, which project strongly and divide rapidly by vertical walls only. The walls of the cells are thickened at the angles, and the surface view is curiously like a cross-section of the collen- chyma of many vascular plants. As in Anthoceros mucilage slits are formed, sometimes on both surfaces of the thallus, and through these the plant is infected with Nostoc, as in the other Anthocerotes. In Dendroceros the Nostoc colonies are very large and cause conspicuous swellings upon the thallus. All the species of Dendroceros that have yet been examined are monoe- cious. The antheridia of Dendroceros (Campbell (20)), which are larger than those of the other two genera, are developed singly in strict acropetal succession, forming a row on each side of the midrib. The youngest ones occur very near the apex of the shoot. The mother cell arises exactly as in Anthoceros and Notothylas, and the periclinal division of the cell lying outside it takes place very early, so that almost from the beginning there are two layers of cells above the antheridial chamber. In all the younger stages met with by the waiter, the antheridium lay horizontally nearly parallel wnth the axis of the shoot, and was attached to the back of the antheridal chamber, instead of at its base, as in the other genera. (Fig. 78, D.) The first division in the antheridium is transverse, and sep- arates the upper part from the stalk. The next divisions may be alike in both of these cells, being vertical walls intersecting so as to divide both cells longitudinally into four similar cells. In the stalk, however, one of these divisions may be suppressed, and in such cases, the stalk has but two rows of cells instead of four. In the ripe antheridium the stalk becomes very long, and is coiled up in the large antheridial chamber. IV. THE ANTHOCEROTES 147 The archegonium of Dendroceros is much hke that of the other genera, perhaps more nearly approaching that of Antho- ceros. The embryo of Dendroceros resembles more nearly that of Anthoceros than it does Notothylas. The archesporium is less a. D. b FiC. yZ.— Dendroceros Breutelii. A, Thallus with sporophyte attached, X4; "B, apex of the thallus X600; C, archegonium, X600; D, E, young antheridia, X600. developed than in either species of Anthoceros that were studied by the writer, showing only an imperfect division into two lay- ers when seen in section. No stomata are developed in the epi- 148 MOSSES AND FERNS CHAE. dermis of the mature sporophyte, which otherwise cidsel}/ resemhles thdit oi Anthoceros. : The spores may remain undivided, as in Anthoceros, or in some species, e. g., D. crispus, they become multicellular before they are discharged. In this respect these species of Dendro- ceros recall Conocephalus and Pellia^ where germination begins before the spores are set free. Notothylas The third genus, Notothylas, is of especial interest, because it was largely upon the results of his investigations upon this Fig. 79. — Dendroceros Breutelii. A, section of young sporophyte, X2S0; B, section of mature sporophyte showing spores and elater-like, sterile cells; C, single elater, X2S0. plant that Leitgeb ( (7), v., p. 39) based his theory of the close relationship of the Anthocerotes and Jungermanniales. All of Leitgeb's observations on the young capsule were made from herbarium material, and, as he himself admits, were in all cases embryos that had not fully developed. The writer has made a very complete examination of the commonest American spe- cies, N. orbicularis (valvata), and the results of the study of the development of the sporogonium differ so much from those of Leitgeb that they will be given somewhat in detail. Mottier IV. THE ANTIIOCEROTES 149 (2) has also studied this species, and his results agree entirely with those of the writer. The thallus much resembles a small Antlioccros, and sec- tions through it show that in its growth and the development and structure of the sexual organs there is close correspondence. The thallus contains very large lacunae, which are formed in pretty regular acropetal order, and vertical sections show these large cavities increasing regularly in size as they recede from the apex. Similar but less regular lacunce occur in A. fiisifor- mis. The antheridia arise as in AntJwceros, endogenously. The youngest stage found is shown in Fig. 80, A. Here evi- F\G. 80. — Notothylas orbicularis. Development of the antheridium. D, cross-section, the others longitudinal sections; E, nearly ripe antheridium, X300, the other fig- ures X600; (^, A, the primary antheridial cells. :%'>mrto\'fv''i* ? . jr'vA -f ' -■5.t'jt ;/^.t5l rj;t dently the young antheridia (c?) have been formed by the longi- tudinal division of a single hypodermal cell, whose sister epider- mal cell has divided again by a transverse wall to form the outer wall of the antheridiaT cavity (Figs. A, B). The commonest' number of antheridia formed is four.''' "~ r:^':.'^n "■^'^ i Less regularity is found in the next divisions than in AnfJio- ceros, although in the main they are the same. This is observ- able both in longitudinal and cross-sections (see Fig. 80, D). 150 MOSSES AND FERNS CHAP. The full-grown antheridium is more flattened than in either species of Anthoceros examined by me, and the stalk shorter and thicker, but otherwise closely resembles it, although the extremely symmetrical arrangement of the cells, especially of the wall, is much less noticeable. The archegonia correspond very closely, both in position and structure, with those of the other genera, the most marked peculiarity being the more nearly equal diameter of the cover cell and central cell, and a corresponding increase in the breadth Fig. 8i. — Notothylas orbicularis. Development of the archegonium, X6oo; x, the apical cell. of the neck canal cell. Subsequently the central cell becomes much enlarged and the appearance of the fully-developed arche- gonium is very much like that of Anthoceros (Fig. 8i, A). As in A. fusiformis, the usual number of neck canal cells seems to be four, and in no case did the number exceed five. The cover cells were four in number in all the archegonia studied, IV. THE ANTIIOCEROTES 151 and are larger than in Anthoccros. As in that genus, they are thrown off when the archegonium opens. Tlie youngest embryo found was composed of four cells, and presented (juite a different appearance from the corre- sponding stage in Anthoceros. It is impossible from this stage to tell whether the first w^all in the embryo is vertical or trans- verse. This embryo consisted of four nearly ecjual quadrants, instead of having the two upper cells larger than the lower ones. By comparison with the older stages there is little doubt that here the first transverse wall separates the foot from the capsule, as in Sphccrocarpus^ and that the upper cell develops directly into the capsule instead of the latter being determined by the second transverse walls. In the next youngest stages Fig. Bs.—'Notothylas orbicularis. A, B, Horizontal sections of the growing point with young archegonia; C, cross-section of the apex of an archegonium, showing the arrangement of the cover cells; D, longitudinal section of a nearly ripe arche- gonium, X400. found (Fig. 83,6) the archesporium was already differentiated. A comparison of this with the corresponding stage of Antho- ceros show^s conclusively that the two are practically identical in structure. The columella, evidently formed as in AiitJio- ceros, and as there made up of four rows of cells, is surrounded by the archesporium cut off from the peripheral cells. Leit- geb's surmise that the columella is a secondary formation is, therefore, for A^. orbicularis at least, entirely erroneous, and it is extremely likely that when normal specimens of the other species are examined from microtome sections, in the young 152 MOSSES AND FERNS CHAP. stages at least, a similar columella will be found. The single embryo that Leitgeb (1. c. PI. IV., Fig. yy) figures of N. orbi- cularis (valvata) is at once seen to be abnormal, and as his con- clusions were drawn from a study of similar dead embryos in the other species, they cannot be accepted without more satis- factory evidence. While in the main corresponding to the em- bryo of Anthoceros there are some interesting differences which are closely associated with the structure of the older sporogo- nium. The foot is smaller than in Anthoceros and derived only from the lowest tier of cells. The columella is decidely smaller, and the archesporium, as well as the young sporogonium wall, relatively much thicker. As in Anthoceros, the archesporium does not extend to the foot, but is separated by the zone of B Fig. 83. — Notothylas orbicularis. A, Four-celled embryo; B, C, older embryos, in longitudinal section. The archesporial cells are shaded. A, X4S0; B, C, X22S. cells which there give rise to the meristem at the base of the capsule. The form of the embryo is different too. It is pear- shaped and more elongated than in Anthoceros. As the embryo develops these differences become more apparent and others arise. Fig. 83, C shows a stage where the division of the archesporial cells has begun, and it is at once apparent how much more conspicuous they are. It is seen too that the outer cells of the upper part of the capsule are also dividing actively, and that, compared with Anthoceros j the IV. THE ANTHOCEROTES 153 apical part of the capsule retains its meristematic character for a much longer period. Corresponding with this, the growth at the base of the capsule is much less marked. The divisions in the archesporium are much more active tlian in Anthoccros, and the apical part of the capsule retains its meristematic char- acter for a much longer period. Corresponding witli tliis, the growth- at the base of the capsule is much less marked. The di- visions in the archesporium are much more active than in An- thoceros, and also less regular. At first divisions occur in the upper portion in all directions, so that above the columella there is a mass of archesporial tissue much thicker than that below, and occupying very much more space than the corresponding tissue in Anthoccros. Longitudinal sections through the basal part of the older sporogonium show an arrangement of tissues similar to those in Anthoccros, but there are differences corre- sponding to those in the young stages. The foot (Fig. 84, A) is much smaller and flatter, and sometimes shows a very regular structure. The central part is composed of a compact mass of rather large cells, between which and the base of the capsule is a narrow zone of meristematic tissue. The superficial cells do not always grow^ out into the root-like processes found in Anthoccros and Dcndroccros, but may remain short and project but slightly. The cells are characterised by abundant granular cytoplasm and conspicuous nuclei, showing that they are prob- ably not only absorbent cells, but also elaborate the food mate- rials taken in from the gametophyte. The gradual transition of the differentiated tissues above into the meristem at the base, is precisely as in Anthoccros, and sections at that point in the two genera can scarcely be distinguished from one another. The columella (in longitudinal section) in both shows four par- allel rows of cells, outside of which lies the single row of arche- sporial cells, and four rows of cells belonging to the wall of the capsule. As the section is examined higher up, however, there are marked differences, especially in the divisions of the arche- sporium. The first divisions in the archesporium of Notothylas are periclinal, and for a short distance it is two-layered, as it is permanently in Anthoccros ; but still further up it widens very rapidly by the formation of repeated periclinal walls, and soon comes to be much thicker than either the columella or the capsule wall. A further study of the developing archesporium shows 154 MOSSES AND FERNS CHAP. e^ <^ J? ^•^ rt V u o o X aj J3 U C •*^ •> (A •— < o o CO X T3 M rt (U ^ u < 3 G « a ■M rt CO e 4) 3 J3 •w C o <*■> bo O o t-i o Fi a to 3 •fH o. • ;-i CO •s Q rt a ^ s pq u • A •** CO 3 CO u i) ■M o «o V w ,__l ?^ rt "««* o llj o O. •kk CO o u C3 ^ J3 O T) 1 B Tf 3 00 .rt O ■♦-* VJ IV. THE ANrilOCEROTES 155 that the divisions occur with a good deal of regularity. The archesporial cells are divided by alternating vertical and trans- verse walls into four layers of cells instead of two, as in Antho- ceros, and these cells are arranged in regularly placed transverse rows. At first the cells appear alike, but later there is a sei)ara- tion into sporogenous and sterile cells as in Anthoccros. Mach primary transverse row of cells becomes divided into two. The upper row grows much faster, and its cells become swollen and the cytoplasm more granular, while the lower row has its cells remaining flattened and more transparent, i. c, there is a sep- aration of the archesporium into alternate layers of sporogenr)us and sterile cells as in Anthoceros, but here the number of cells is double that in the latter, and the longer axis of the cells is transverse instead of vertical. In the portion of the archesporium above the columella these alternate layers of spore mother cells and sterile cells extend com- pletely across, and Leitgeb has correctly fig- ured this, although he probably was mistaken in assuming that this arrangement extended to the base of the capsule. The further development of the capsule is much like that of Anthoceros, but the division of the chloroplast takes place before the spore mother cells are isolated, and the primary chlo- roplast is evident almost as soon as the sporog- enous cells are recognisable as such. The cells of the columella do not become as elon- gated as in Anthoceros, and develop thicken- ings much like those of the sterile cells of the archesporium; and it was this partly that led Leitgeb to the conclusion that even where a definite columella was present it probably arose as a secondary formation in the archesporium, similar to the formation of the axial bundle of elaters in Pellia, and that in Notothylas as in the Jungermanniales, the archesporium arose from the inner of the cells formed by the first periclinal w^alls, and not from the outer ones. That this is not true for A'', oribictdaris is shown beyond question from sections of both the older and younger sporogonium, and it would be Fig. 85. — Longitu- dinal section of a nearly ripe sporo- gonium of N. or- bicularis, Xso. 156 MOSSES AND FERNS chap. extremely strange if the other species should differ so radically from this one as would be the case were Leitgeb's surmise correct. The wall of the capsule does not develop the assimilative apparatus of the Anthoceros capsule, and stomata are com- pletely absent from the epidermis. The inner layers of cells are more or less completely disorganised, and they probably serve to nourish the growing spores, which here, of course, are correspondingly more numerous than in Anthoceros. As in the latter the sterile cells from a series of irregular chambers in which the spores lie. At maturity these sterile cells separate into irregular groups. Their walls are marked with short curved thickened bands, yellowish in colour like the wall of the ripe spores. At maturity the capsule projects but little beyond its sheath, and opens by two valves. In some species, e. g., N. melanospora, the capsule often opens irregularly. The Evolution of the Anthocerotes The Anthocerotes form a most interesting series of forms among themselves, but are also of the greatest importance in the study of the origin of the higher plants. Unquestionably Notothylas represents the form which most nearly resembles the other Liverworts, but until the other species are investigated further we shall have to assume that the type of the sporo- gonium is essentially different from that of the lower Hepaticse, and corresponds to that of the other Anthocerotes. The pri- mary formation of the columella and the subsequent differentia- tion of the archesporium occur elsewhere only in the Sphagna- cese. From Notothylas, where the archesporium constitutes the greater part of the older sporogonium, and the columella and wall are relatively small, there is a transition through the forms w^th a relatively large columella to Dendroceros, where the spore formation is much more subordinated and a massive assimilative tissue developed. In Notothylas the secondary growth of the capsule at the base, while it continues for some time, is checked before the capsule projects much beyond its sheath. In Dendroceros the growth continues much longer, although it does not continue so long as in Anthoceros. The assimilative system of tissue in the latter is finally completed by the development of perfect stomata, and the growth of the IV. THE ANTIIOCEROTES 157 capsule is unlimited. All that is needed to make the sporo- phyte entirely independent is a root connecting- it with the earth. The Inter-rclationships of the Ilcpaticcc From a review of the preceding account of the Liverworts, it will be apparent that these plants, especially the thai lose forms, constitute a very ill-defined group of organisms, f;ne set of forms merging into another by almost insensible gradations, and this is not only true among themselves, but applies also to some extent to their connection with the M(jsses and Pteridophytes. The fact that the degree of development of gametophyte and sporophyte does not always correspond makes it very difficult to determine which forms are to be regarded as the most primitive. Thus while Riccia is unquestionably the simplest as regards the sporophyte, the gametophyte is very much more specialised than that of Aneura or Sphccrocarpus. The latter is, perhaps, on the whole the simplest form we know, and we can easily see how from similar forms all of the other groups may have developed. The frequent recurrence of the two-sided apical cell, either as a temporary or permanent con- dition in so many forms, makes it probable that the primitive form had this type of apical cell. From this hypothetical form, in which the thallus w-as either a single layer of cells or with an imperfect midrib like Sphcerocarpiis, three lines of development may be assumed to have arisen. In one of these the differenti- ation was mainly in the tissues of the gametophyte, and the sporophyte remained comparatively simple, although showing an advance in the more specialised forms. The evolution of this type is illustrated in the germinating spores of the Mar- chantiacea^, w^here there is a transition from the simple thallus with its single apical cell and smooth rhizoids to the complex thallus of the mature gametophyte. In its earlier phases it re- sembles closely the condition which is permanent in the simpler anacrogynous Jungermanniacese, and it seems more probable that forms like these are primitive than that they have been de- rived by a reduction of the tissues from the more specialised thallus of the Marchantiacese. Sphcerocarpiis, showing as it does points of affinity wuth both the lower Marchantiales and the anacrogynous Jungermanniales, probably represents more nearly than any other known form this hypothetical type. Its 158 MOSSES AND FERNS chap. sporogonium, however, simple as it is, is more perfect than that of Riccia, and if our hypothesis is correct, the Marchanti- ales must have been derived from Sphcurocarpus-likQ forms in which the sporophyte was still simpler than that of existing species. Assuming that this is correct, the further evolution of the Marchantiales is simple enough, and the series of forms from the lowest to the highest very complete. In the second series, the Jungermanniales, starting with Sphcerocarpus, the line leads through Aneura, Pellia, and simi- lar simple thallose forms, to several types with more or less perfect leaves— ^.^.^ Blasia, Fossombronia, Treuhia, Haplomit- rium. These do not constitute a single series, but have evi- dently developed independently, and it is quite probable that the typical foliose Jungermanniacese are not all to be traced back to common ancestors, but have originated at different points from several anacrogynous prototypes. The systematic position of the Anthocerotes is more diffi- cult to determine, and their connection with any other existing forms known must be remote. While the structure of the thal- lus and sporogonium in Notothylas shows a not very remote resemblance to the corresponding structures in Sphcerocarpus, it must be remembered that the peculiar chloroplasts of the Anthocerotes, as well as the development of the sexual organs, are peculiar to the group, and quite different from other Liver- worts. To find chloroplasts of similar character, one must go to the green Algae, where in many Confervacese very similar ones occur. It is quite conceivable that the peculiarities of the sexual organs may be explained by supposing that those of such a form as Sphcero carpus, for example, should become co- herent with the surrounding envelope at a very early stage, and remain so until maturity. In Aneura we have seen that the base of the archegonium is confluent with the thallus, in which respect it offers an approach to the condition found In the An- thocerotes; but that this is anything more than an analogy is improbable. The origin of the endogenous antheridium must at present remain conjectural, but that it is secondary rather than primary is quite possible, as we know that occasionally the antheridium may originate superficially. In regard to the sporogonium, until further evidence is brought forward to show^ that Nofothylas may have the columella absent in the early stages, it must be assumed that its structure in the Anthocerotes IV. THE ANTHOCEROTES i59 is radically different from that of the other Liverworts. Of the lower Hepaticae Sphccrocarpiis perhaps offers again the nearest analogy to Notothylas, but it would not be safe at present to assume any close connection between the two. Of course the very close relationships of the three genera of the Anthocerotes among themselves are obvious. On the whole, then, the evidence before us seems to indicate that the simplest of the existing Hepaticse are the lower thallose Jungermanniales, and of these Sphcorocarpiis is probably the most primitive. The two lines of the Marchantiales and Jun- germanniales have diverged from this common ancestral type and developed along different lines. The Anthocerotes cannot certainly be referred to this common stock, and differ much more radically from eitl:er of the other two lines than these do from each other, so that at present the group must be looked, upon as at best but remotely connected with the other Hepaticae, and both in regard to the thallus and sporophyte has its nearest affinities among certain Pteridophytes. The possibility of sep- arate origin of the Anthocerotes from Coleochcete-Wke ancestors is conceivable, but it seems more probable that they have a com- mon origin, very remote, it is true, with the other Liverworts. They may probably best be relegated to a separate class, coordi- nate with the Hepaticae and Musci. CHAPTER V THE MOSSES (MUSCI) : SPHAGN ALES— ANDREW ALES The Mosses offer a marked contrast to the Hepaticse, for while the latter are pre-eminently a generalised group, the Mosses with a very few exceptions form one of the most sharply defined and specialised groups of plants known to us. Although much outnumbering the Liverworts in number of species, as well as individuals, the differences in structure be- tween the most extreme forms are far less than obtain among the Liverworts. While the latter occur as a rule in limited numbers, and for the most part where there is abundant moisture, the Mosses often cover very large tracts almost to the exclusion of other vegetation, especially in northern countries. In more temperate regions, the familiar peat-bogs are the best known examples of this gregarious habit. Mosses are for the most part terrestrial, and are found in almost all localities. Some grow upon organic substrata, especially de- caying wood, and are to a greater or less extent saprophytic. Haberlandt (4) first called attention to this, and investigated a number of forms, among them Rhynchosfegium murale, Eurynchhtm prcelongum, Wehera nutans, and others, and in these found that the rhizoids had the power of penetrating the tissue of the substratum, much as a fungus would do. The most remarkable case, however, is Buxhaumia, where the leaves are almost completely absent and the saprophytic habit very strongly pronounced. . Most of the Mosses, however, are abundantly provided with assimilative tissue, and grow upon almost every substratum, although most of them are pretty constant in their habitat. A number of species are typically aquatic, e. g., Fontinalis and many species of Sphagnum and 160 CH.v. MOSSES (MUSCI): SPHAGN ALES— ANDRE.^ALES i6i Hypmim; others grow regularly in very exposed situations on rocks, e. g., Andrecea. Very many, like Funaria hygrometrica and Atrichmn undiilatiini, grow upon the earth ; and others again, like species of Mniiun and Thuidiuni, seem to grow exclusively upon the decaying trunks of trees. Indeed Mosses are hardly absent from any locality except salt water. With the exception of the Sphagnaceae and Andreaeacese, and pos- sibly Archidium, the type of structure found among the Mosses is extraordinarily constant, and they may all be unhesitatingly referred to a single order, the Bryales, which includes within it an overwhelming majority of the species. The gametophyte of the Musci always shows a well- marked protonema, which in most cases has the form of an extensively branching alga-like filamentous structure, from which later a distinct leafy axis arises as a lateral bud. In Sphagnum this protonema is a flat thallus, and the same is true of TetrapJiis and a few other forms, but the filamentous proto- nema is very much more common. The gametophore arises from this protonema as a lateral bud, which develops a pyramidal apical cell, from which three sets of segments are cut off, each segment producing a leaf. The only exception to this, so far as is known at present, is the genus Fissidens (Leitgeb (2)), where the apical cell is wedge-shaped, and only two sets of segments are formed. Upon these leafy branches the sexual organs are borne. The relative degree of development of the protonema and the gametophore differ much in different forms. Thus in the Phascacese the proto- nema is permanent, and the gametophore small and poorly developed. In the higher Mosses the protonema disappears more or less completely, and the assimilative functions are entirely assumed by the large highly developed gametophore, which is capable of reproducing itself by direct branching without the intervention of the protonema. The commonest type of gametophore is the upright stem with the leaves ar- ranged radially about it, but in many creeping forms, such as some species of Mnhim, Hypmim, etc., the gametophore is more or less dorsiventral ; but in these the apical cell is pyram- idal, and produces three rows of leaves. Growing out from the base of the stem in most Mosses, and fastening it to the substratum, are numerous brown rhizoids which are not, how- ever, morphologically distinct from the protonema. Thus if II i62 MOSSES AND FERNS chap. a turf of growing Moss is. turned upside down, the rhizoids thus exposed to the hght very soon develop chlorophyll, and grow out into normal protonemal filaments. In most of the Mosses the leaves show a one-layered lamina traversed by a midrib, which may be quite small or very massive. This midrib is made up in part of elongated thick- walled sclerenchyma, and contains a conducting tissue. The highest grade of development of the leaf is met with in the PolytrichacecEj where the midrib is very massive and peculiar vertical laminae of chlorophyll-bearing cells grow out from the surface of the leaf. In Bnxbaumia the leaves are almost en- tirely abortive. The peculiar leaves of Sphagnum will be re- ferred to later, as well as the details of structure of the leaves of other forms. The stem, except in the lowest forms, is traversed by a well-defined central strand of conductive tissue, and in a few of the highest ones, e. g. Polytrichum, there are in addition smaller bundles, continuations of the midribs of the leaves, recalling the "leaf-traces" found in the stems of Spermato- phytes. The types of non-sexual reproduction among the Musci are extraordinarily various, and a careful study of them shows that the morphological connection between the protonema and gametophore is a very intimate one, as they may arise recip- rocally one from the other. With the exception of certain resting buds developed from the protonema it appears (Goebel (lo), p. 170) that the formation of the leafy stem is always preceded by the protonema. The latter arises primarily from the germinating spores, but may develop secondarily from almost any part of the gametophore or even in exceptional cases from the cells of the sporophyte (Pringsheim (2) ; Stahl (i)). From these protonemal filaments new gameto- phores arise in the usual way. The gametophore itself, es- pecially where it is large and long lived, by the separation of its branches rapidly increases the number of new individuals. This is especially marked in Sphagnum, where this is the principal method of propagating the plants. Special organs of propagation in the form of gemmse also occur, and these may develop from the protonema or from the gametophore Tetraphis pellucida (Fig. 118) is a good example, showing these specialised gemmse which after a time germinate by V. MOSSES (MUSCI): SPHAGN ALES— ANDRE/HALES 163 giving rise to a protonema upon which, as usual, the gameto- phore arises as a bud. In size the gametophore of the Mosses ranges from a milHmetre or less in height in Biixbaiimia and Ephemerum to 30 to 50 cm. in the large Polytrichacese and Fontinalis. The branching of the gametophore. is never dichotomous, and so far as is known the lateral branches arise, not in the axils of the leaves, but below them. Underground t , C^' %v ^' /IS '- Fig. 86. — Climacium Americanum, showing the formation of stolons, Xi» Stems or stolons, which afterwards develop into normal leafy axes, are common in many forms, e. g., Climacium (Fig. 86). The sexual organs are borne either separately or together at the summit of the gametophoric branches. Where the plants are dioecious, it sometimes happens that the two sexes do not grow near together, in which case, although archegonia i64 MOSSES AND FERNS CHAP. may be plentiful, they fail to be fecundated and thus no cap- sules are developed. This no doubt accounts for the extreme rarity of the sporogonium in many Mosses, although in other cases, e. g., Sphagnum, it would appear that the formation of the sexual organs is a rare occurrence. These resemble in gen- eral those of the Hepaticse, but differ in some of their details. The leaves surrounding them are often somewhat modified, and in the case of the male plants (Atrichum, Polytrichum) different in form and colour from the other leaves, so that the whole structure looks strikingly like a flower. As a rule, the archegonial receptacles are not so conspicuous. The early divisions of the archegonium correspond closely with those of the Liverworts, but after the ''cover cell" is formed, instead of dividing by cross walls into four cells, it functions for some time as an apical cell, and to its activity is largely due the fur- ther development of the neck. The venter is usually very much more massive than in the Hepaticse, and the egg small. The antheridia, except in Sphagnum, are borne also at the apex of the stem, whose apical cell does not always, at any rate, become transformed into an antheridium, as we sometimes find, especially in species of Atrichum and Polytrichum, that the axis grows through the antheridial group and develops a leafy axis, which later may form other antheridia at its apex. Where the plants are dioecious the males are usually noticeably smaller than the females. The antheridia, except in Sphagnum, are very uniform in structure, and like the archegonium exhibit a very definite apical growth (Fig. 102). The wall remains one-layered, as in the Liverworts, and often the chromatophores in its cells become red at maturity, as in some Liverworts, e. g., Anthoceros. The ripe antheridium is in most Mosses club- shaped, and the sperm cells are discharged while still in con- nection, the complete isolation of the sperm cells only taking place some time after the mass has lain in water. In Sphag- num the antheridia are much like those of certain leafy Liver- worts, and stand singly in the axils of the leaves of the male branches. Holferty ( i ) describes and figures a number of interesting abnormalities in Mnium cuspidatum in which organs are some- times developed which are intermediate in character between archegonia and antheridia. The sporophyte of the Mosses reaches a high degree of V. MOSSES (MUSCI): SPHAGNALES—ANDREJEAl.ES 165 development in the typical forms, and shows great uniformity, both in its development and in the essential structure of the full-grown sporophyte. With the exception of Splicr^iiion, which will be referred to more specially later, the early growth of the sporogonium is due to the segmentation of a two-sided apical cell. The separation of the archesporium takes place at a late period, and like that of Anthoccros it occupies but a very small part of the sporogonium, which in all the liigher forms attains a considerable size and comi)lexity. All the archesporial cells form spores, and no trace of elaters can be found. In all but the lower types, the sporogonium becomes differentiated into a stalk (seta) and a capsule. This differ- entiation is gradual, and the elongation of the seta is not a rapid process, due simply to an elongation of the cells, but is caused by actual growth and cell division. In Sphagnum and Andrecea, where no seta is present, the axis of the gameto- phore elongates and forms a sort of stalk (pseudopodium), which carries up the capsule above the leaves. The formation of the capsule and seta takes place by a rapid enlargement of the upper part of the very much elongated embryo about the same time that the archesporium becomes recognisable. This enlargement is accompanied by a separa- tion of the cells of two layers of the wall, by w^hich an inter- cellular space is formed which later may become very large (Figs. 109-112). A second similar space may be developed in- side the archesporium, but this is found only in the Polytrich- aceae. In the Sphagnacese and the Andreseacese this space is not developed. These lacunae are traversed by protonema-like filaments of chlorophyll-bearing cells, and the cells of the mass- ive wall of the capsule also contain much chlorophyll, so that there is no question that the sporogonium is capable of assimila- tion. Stomata, much like those of AntJwceros or the vascular plants, occur upon the basal part of the capsule in many species, but are not always present. In Sphagnum and all the higher Bryales the capsule opens regularly by means of a circular lid or operculum. This in the latter group is a most characteristic structure, and with its accompanying structures, the "annulus" and "peristome," form some of the most important distinguishing marks of different genera and species. When ripe, the operculum falls off and the ripe spores are set free. The teeth of the peristome, by i66 MOSSES AND FERNS chap. their hygroscopic movements, play an important part in scat- tering the spores, and physiologically take the place of the elaters of the Hepaticse. Some Mosses live but a few months, and after ripening their spores, die. This is the case with Funaria hygrometrica, at least in California. Other Mosses are perennial, and some species of peat or tufa-forming Mosses seem to have an un- limited growth, the lower portions dying and the apices grow^ ing on until layers of peat or tufa of great thickness result, covered over with the still living plants whose apices are the direct continuation of the stems which form the basis of the mass. With the exception of a very few forms all the Mosses are readily referable to three orders. The first two, the Sphagnales and the Andreaeales, are represented each by a single genus, and are in several respects the types that come nearest the Liver- worts. All the other Mosses, except perhaps Archidium and Buxhaumia, conform to a very well-marked type of develop- ment, and may be referred to a common order, the Bryales. The Phascacese or cleistocarpous Mosses are sometimes sep- arated from the higher Bryales as a distinct order, but a study of their development shows that they belong to the same series, and only differ in the degree of development from the more specialized stegocarpous forms. Order I. — Sphagnales The Sphagnales, or Peat-Mosses, are represented by the single genus Sphagnum. They are Mosses of large size, which, as is well known, often cover large tracts of swampy land and about the borders of lakes, forming the familiar peat- bogs of northern countries. Owing to the empty cells in the leaves and outer layers of the stem, they suck up water like a sponge, and the plants when growing are completely saturated with water. The colour is usually pale green, but varies much in depth of colour, and in many species is red or yellow. When dry the colour is much duller, largely owing to the opacity of the dry, empty cells which conceal to a great extent the colour of the underlying tissues. They branch extensively, and, ac- cording to Schimper, a branch is always formed corresponding to every fourth leaf ; but Leitgeb has shown that although this V. MOSSES (MUSCI): SPHAGN ALES— ANDREW ALES 167 is the rule numerous exceptions to it occur. In sterile plants the branches are of two kinds, long flagellate branches which hang down almost vertically and are applied to the stem, and much shorter ones that are crowded together at the apex and have only a limited growth. The leaves are inserted on the Fig. B7.^'Sphagnutn (sp); A, B, Young protonemata, X262; C, an older protonema with a leafy bud (fe), X about 40; r, marginal rhizoids. Stem by a broad base, and taper to a more or less well-marked point. According to Schimper, the divergence of the leaves of the main axis is always two-fifths, but on the smaller branches variations from this sometimes occur. The leaves i68 MOSSES AND FERNS CHAP. sp show no trace of a midrib. As the axis elongates the leaves become separated, as well as the lower branches, but upon the smaller branches they remain closely imbricated. Rhizoids are present only in the earlier stages of the plant's growth, and are only occasionally found in a very rudimentary condition in the older ones. The spores of Sphagnum on germination form first a very short filament, which soon, at least when grown upon a solid substratum, forms a fiat thallus, which at first sometimes grows by a definite apical cell (C. Muller (3)). It first has a spatu- late shape (Fig. 87, A, B), which later becomes broadly heart-shaped, and closely resembles in this condi- tion a young Fern prothallium, for which it is readily mistaken. The older ones become more irregular and may attain a diameter of sev- eral millimetres. The thallus is but one cell thick throughout its whole extent, and is fastened to the earth by colourless rhizoids. Later similar filaments grow out from the marginal cells of the thallus, and a careful examination shows that they are septate, and closely re- semble the protonemal filaments of other Mosses. Like those, the Fig. z%. — sphagnum squarrosum. g^p^^ especially in the colourlcss Leafy shoot with sporophytes ^ ^ -^ (sp), borne at the end of leaf- oues, are strougly obliquc. ihese less branches, or "pseudopodia," marginal protoucmal threads may, according to Hofmeister (i) and Schimper (i), produce a flattened thallus at their extremity, and thus the number of fiat thalli may be increased. Schimper states that if the germination takes place in water, the forma- tion of a fiat thallus is suppressed and the protonema remains filamentous, but Goebel disputes this. In the few cases observed by me, only one leafy axis arose from each thalloid protonema, and although this is not expressly stated by Hofmeister and Schimper, their figures would indi- cate it. At a point, usually near the base, a protuberance is ■"^ V. MOSSES (MUSCI): SPHAGNALES—ANDREALALES 169 formed by the active division of the cells, in a manner probably entirely similar to that in other Mosses, and this rapidly as- sumes the form of the young stem. The first leaves are very simple in structure, and are composed of perfectly uniform elongated quadrilateral cells, all of which contain more or less chlorphyll. Like the older ones, however, they show the char- acteristic two-fifth divergence. Schimper states that the fifth leaf, at the latest, shows the differentiation into chlorophyll- A. Fig. 89. — Sphagnum cymbifolium. A, Median longitudinal section of a slender branch; X, the apical cell; B, part of a section of the same farther down, showing the enlarged cells at the bases of the leaves, and the double cortex (cor) ; C, cross- section near the apex of a slender branch; D, glandular hair at the base of a young leaf — all X525. bearing and hyaline cells, found in the perfect leaves. The first leaves in which this appears only show it in the lower part the cells of the apex remaining uniform. 170 MOSSES AND FERNS chap. At the base of the young plant very deHcate colourless rhizoids are developed, and these show the oblique septa so general in the rhizoids of other Mosses. As the plant grows older these almost completely disappear. The apex of the stem and branches is occupied by a pyram- idal apical cell with a very strongly convex outer free base. From the lateral faces of the apical cell, as in the acrogynous Liverworts, three sets of segments are formed. The whole vegetative cone is slender, especially in the smaller branches. The first division in the young segment is parallel to its outer face, and separates it into an inner cell, from which the central part of the axis is formed, and an outer cell which produces the leaves and cortex. The second wall, which is nearly horizontal, divides the outer cell of the segment into an upper and a lower cell, the former being much broader than the latter, which is mainly formed from the kathodic half of the segment, which is higher than the anodic half (Leitgeb (i)). The next wall divides the upper cell into an upper and a lower one, the former being the mother cell of the leaf, the lower, with the other basal cell, giving rise to the cortex. Growth proceeds actively in the young leaf, which soon projects beyond the surface of the stem, and by the formation of cell walls perpendicular to its surface forms a laminar projection. The position of the cell walls in the young leaf is such that at a very early period a two-sided apical cell is established, which continues to function for a long time, and to whose regular growth the symmetrical rhomboidal form of the cells of the young leaf is largely due (Fig. 90). The leaves do not retain their original three-ranked arrange- ment, but from the first extend more than one-third of the cir- cumference of the stem, S"o that their bases overlap, and the leaves become very crowded, and the two-fifth arrangement is established. The degree to which the central tissue of the stem is developed varies with the thickness of the branch. In the main stem it is large, but in the small terminal branches it is much less developed, as well as the cortex, which in these small branches is but one cell thick. Later the cortex of the large branches becomes two-layered (Fig. 89, B), and is clearly sep- arated from the central tissue, whose cells in longitudinal sec- tion are very much larger. In such sections through the base V. MOSSES (MUSCI): SPHAGN ALES— ANDRE JEALES 171 of very young leaves characteristic glandular hairs are met with. They consist of a short basal cell and an enlarged ter- minal cell containing a densely granular matter, which from its behaviour with stains seems to be mucilaginous. The form 172 MOSSES AND FERNS chap. of the secreting cell is elongated oval (Fig. 89, D), and the hair is inserted close to the base of the leaf, upon its inner sur- face. The young leaf consists of perfectly uniform cells of a nearly rhomboidal form (Fig. 90, A), and this continues until the apical growth ceases. Then there begins to appear the sep- aration into the chlorophyll-bearing and hyaline cells of the mature leaf. This can be easily followed in the young leaf, where its base is still composed of similar cells, but where toward the apex the two sorts of cells become gradually differ- entiated. The future hyaline cells grow almost equally in length and breadth, although the longitudinal growth some- what exceeds the lateral. These alternate regularly with the green cells, which grow almost exclusively in length, and form a network with rhomboidal meshes, whose interstices are occu- pied by the hyaline cells. The latter at first contain chloro- phyll, which soon, however, disappears; and finally, as is well known, they lose their contents completely, and in most cases round openings are formed in their walls. The protoplasm is mainly used up in the formation of the spiral and ring-shaped thickenings upon the inner surface of the wall, so characteristic of these cells (Fig. 90, D). The chlorophyll cells are some- times so crowded and overarched by the hyaline ones that they are scarcely perceptible, and of course in such leaves the green colour is very faint. Cross-sections of the leaves show a char- acteristic beaded appearance, the large swollen hyaline cells regularly alternating with the small wedge-shaped sections of the green cells (Fig. 90, E). Russow (4) has shown that the leaves of the sporogonial branch retain more or less their primi- tive character, and the division into the two sorts of cells of the normal leaves is much less marked. He connects this with the necessity for greater assimilative activity in these leaves for the support of the growing sporogonium. From his account too it seems that the stem leaves lose their activity very early. The degree of development of the thickenings upon the walls of the hyaline cells varies in different species, and in dif- ferent parts of the leaf. It is, according to Russow, best de- veloped in the upper half of the leaf, where these thickenings have the form of thin ridges projecting far into the cell cavity. The development of the central tissue of the stem varies. V. MOSSED (MUSCI): SPIIAGNALES—ANDREALALES i73 The central portion usually remains but little altered and con- stitutes a sort of pith composed of thin-walled colourless par- enchyma, which merges into the outer prosenchymatous tissue of the central region. The cells of the latter are very thich walled, and elongated, and their walls are usually deeply stained with a brown or reddish pigment. In their earlier stages, ac- cording to Schimper ((i), p. 36), the prosenchyma cells have regularly arranged and characteristic pitted markings on their walls, but as they grow^ older and the walls thicken, these be- come largely obliterated. Cross-sections of these prosenchyma cells show very distinct striation of the w^all (Fig. 90, G), which become less evident as they approach the thinner-walled parenchyma of the central part of the stem. No trace of a cen- tral cylinder of conducting tissue, such as is found in most of the Mosses, can be found in Sphagnum, and this is correlated with the absence of a midrib in the leaves. The cortex at first forms a layer but one cell thick, but is from the first clearly separated from the axial stem tissue. In the smallest branches it remains one-layered (Fig. 89, C), but in the larger ones it early divides by tangential walls into two layers, which at this stage are very conspicuous (Fig. 89, B). Later there may be a further division, so that the cortex of the main axes frequently is four-layered. While the cells of the young cortex are small, and the tissue compact, later there is an enormous increase in the size of the cells, which finally lose their protoplasmic contents and resemble closely the hyaline cells of the leaves. Like the latter, the cortical cells are per- fectly colourless, and usually have similar circular perforations in their walls. The resemblance is still more marked in S. cymhifolinm, where there are spiral thickened bands, quite like those of the hyaline leaf cells. On the smaller branches the cortical cells (Schimper (i), p. 39), have been found to be of two kinds — the ordinary form and curious retort-shaped cells with smooth walls and single terminal pore. The Branches Leitgeb ( i ) has studied carefully the branching of Sphag- num, which corresponds closely to the other Mosses investi- gated. The branch arises from the lower of the two cells into 174 MOSSES AND FERNS chap. which the outer of the two primary cells of the segment is divided. In this cell, which ordinarily constitutes part of the cortex, walls are formed in such a way that an apical cell of the ordinary form is produced. These lateral branches themselves branch at a very early period, and form tufts of secondary ones. Schimper was unable to make out clearly what the nature of this branching was, but suggested a possible dichotomy. Leit- geb, however, concludes that it is monopodial, and that each branch corresponds to a leaf, as do the primary branches. The growth of all the lateral branches, both the descending flagellate ones and the short upright ones at the top of the stem, is limited, and lasts through one vegetative period only. This, however, is not true of the branches that are destined to continue the axis These are apparently morphologically the same as those whose growth is limited, but they continue to grow in the same man- ner as the main axis. The Sexual Organs The sexual organs in Sphagnum are produced on branches that do not differ essentially from the sterile ones. The leaves of the antheridial branches are usually brightly coloured, — red, yellow, or dark green, and are closely and very regularly set so that the branch has the form of a small catkin (Fig. 91, A). The antheridia stand singly in the axils of the leaves, and Leit- geb states that their position corresponds with that of branches, with which he regards them as homologous, having observed in some cases a bud occupying the place of an antheridium. He studied in detail their development, which differs considerably from that of the other Mosses. The antheridium arises from a single cell whose position corresponds to that of a lateral bud on an ordinary branch. This cell grows out into a papilla and becomes cut ofiF by a transverse wall. The outer cell continues to elongate without any noticeable increase in diameter, and a series of segments are cut off from the terminal cell by walls parallel to its base, so that the young antheridium consists of simply a row of cells, comparable to the very young anther- idium of the Marchantiacese. Intercalary transverse divisions may also arise, and later some or all of the cells, except the ter- minal one, divide by longitudinal walls, usually two intersect- ing ones in each cell, so that the antheridium rudiment at this V. MOSSES (MUSCI): SPHAGNALES—ANDREJEALES 175 stage is composed of a long stalk composed of several rows of cells, usually four, and a terminal cell which later gives rise to .-cal Fig. 91. — A, Male catkin of Sphagnum cymhifoUum, X50; B, young antheridium of S. acutifolium, X350; C, opened antheridium of the same species; D, spermatozoid, Xiooo (about); E, female branch with sporogonium of S. acutifolium, slightly magnified; cal, calyptra. A, C, E, after Schimper; B, after Leitgeb. the body of the antheridium. The first divisions in the body of the antheridium only take place after the stalk has become 176 MOSSES AND FERNS chap. many times longer than the terminal cell, and is divided into many cells. The account of the development of the antheridium given by Hofmeister and Schimper is incomplete, and differs in some respects from that of Leitgeb. Neither of the former observ- ers seems to have clearly recognised the presence of a definite apical cell from the first. Schimper ( ( i ) , p. 45 ) , states that after the stalk has been formed four rows of segments arise from the terminal cell; to judge from the somewhat vague statements of Hofmeister ((i), p. 154), it appears that he re- garded the terminal growth as taking place by the activity of a two-sided apical cell, as in other Mosses. Leitgeb states that, while this form of growth does frequently occur, usually the divergence of the segments is not exactly half, and the segments do not stand in two straight rows, but some of them are inter- calated between these, forming an imperfect third row. Each segment is first divided by a radial wall into nearly equal parts, and these are then divided into an outer and an inner cell, and from the latter by repeated divisions the sperm cells are formed. The body of the full-grown antheridium is broadly oval, and both in its position and shape recalls strongly that of such a foliose Liverwort as Porella. The development of the spermatozoids has been carefully followed by Guignard ((i), p. 69), and corresponds in the main with that of the Hepaticae. A peculiar feature is the presence of a pear-shaped amylaceous mass, firmly attached to the posterior coil. This becomes evident at a very early stage in the development and remains unchanged up to the time the spermatozoids are liberated (Fig. 91, D). The vesicle in which it is enclosed collapses, leaving only the large starch granule, which finally becomes detached. The free spermato- zoid has about two complete coils, and in form recalls that of Chara. The cilia are two and somewhat exceed in length the body. The ripe antheridium is surrounded by a weft of fine branching hairs, which Schimper suggests serve to supply it with moisture.^ It opens by a number of irregular lobes (Fig. 91, C), precisely as in Porella, and, like that, the swelling of the cells is often so great that some of them become entirely ^ These are probably the hyphae of a fungus, V. MOSSES (MUSCI): SPHAGNALES—ANDRE^ALES \77 detached. Schimper states that antheridia may l:>e formed at any time, but they are more abundant in the late autumn and winter. The archegonia are found at the apex of some of the short Fig. 92. — Sphagnum acutifolium. Development of the embryo (after Waldner). A-D, Median optical section; E, F, cross-sections. A, D, E, F, X360; C, X315; D, XiS3. branches at the summit of the plant, which externally are indis- tinguishable from the sterile branches. The development of the archegonia has not been followed completely, but to judge from the stages that have been observed and the mature arche- 12 178 MOSSES AND FERNS chap. gonium, its structure and development correspond closely to that of the other Mosses. As in these, and the acrogynous Hepaticse, the apical cell of the branch becomes an archegonium, and a varying number of secondary archegonia arise from its last-formed segments. The mature archegonium has a mass- ive basal part and long somewhat twisted neck, consisting of six rows of cells. As in the other Mosses, the growth of the young archegonium is apical, and probably as there the neck canals are formed as basal segments of the apical cell, and the ventral canal cell is cut off from the central cell in the usual way. The venter merges gradually into the neck above and the pedicel below^ and at maturity its wall is two or three cells thick. The Qgg (Waldner (2)) is ovoid, and the nucleus shows a distinct nucleolus. Whether a receptive spot is present is not stated. Mixed with the archegonia are numerous fine hairs like those about the antheridium. The leaves immedi- ately surrounding the group of archegonia later enlarge much and form a perichsetium. By the subsequent elongation of the main axis both archegonial and antheridial branches are often separated by the growth of the axis between them, al- though at first they are always crowded together at the top of the main stem. The Sporophyte Waldner (2) has recently studied carefully the develop- ment of the embryo of Sphagnum, which differs essentially from all the other Mosses, and has its nearest counterpart in the Anthocerotes. In the species S. acutifolium, mainly studied by Waldner, the sexual organs are usually mature in the late au- tumn and winter, and fertilisation occurs early in the spring. The ripe sexual organs are found in a perfectly normal condi- tion in mid-winter, under the snow, and apparently remain in this condition until the first warm days, when they open and fertilisation is effected. The first embryos were found late in February, and development proceeded from that time. The first division in the embryo is horizontal and divides it into two cells. In the lower of these the divisions are irregu- lar, but in the upper one the cell walls are arranged with much regularity. The upper cell is the apical cell of the young em- bryo, and from it, by walls parallel to the base, a series of seg- V. MOSSES (MUSCI): SPHAGNALES—ANDRE/EALES i79 ments is formed (Fig. 92, A). These are usually about seven in number, and each of these segments undergoes regular divi- sions, these beginning in the lower ones and proceeding toward the apical cell, which finally ceases to form basal segments and itself divides in much the same way as the segments. The latter first divide by two vertical divisions into quadrants, and in each quadrant either directly l)y periclinal walls, or by an anticlinal wall followed by a periclinal wall in the inner of the two cells (Fig. 92, E), four central cells in each segment are separated from four or eight peripheral ones. The terms cn- dotheciuni and amphithccium have been given respectively to these two primary parts of the young Moss-sporogonium. By the time that the separation of endothecium and amphithecium is completed, a division of the embryo into two regions becomes manifest (Fig. 92, C). Only the three upper segments, in- cluding the apical one, give rise to spores ; the lower segments together with the original basal cell of the embryo form the foot, which in Sphagmim is very large. The cells of the foot enlarge rapidly and form a bulbous body very similar in appear- ance and function to that of Notothylas or Anthoccros. The next divisions too in the upper part of the sporogonium find their nearest analogies in these forms. The central mass of cells, both in position and origin, corresponds to the columella in these genera, and the archesporium arises by the division of the amphithecium into two layers by tangential walls, and the inner of these tw^o layers, in contact with the columella, becomes at once the archesporium. By rapid cell division the upper part of the sporgonium becomes globular, and is joined to the foot by a narrow neck, much as in Notothylas (Fig. 93). The single-layered wall of the young sporogonium becomes six or seven cells thick, and the columella very massive. The one- layered archesporium also divides twice by tangential walls, and thus is four-layered at the time the spore mother cells sep- arate. i\ll the cells of the archesporium produce spores of the ordinary tetrahedral form. The so-called ''microspores" have been shown conclusively to be the spores of a parasitic fungus (Nawaschin (i)). The layer of cells in immediate contact with the archesporium on both inner and outer sides has more chlorophyll than the neighbouring cells, and forms the "spore-sac." i8o MOSSES AND FERNS CHAP. The ripe capsule opens by a circular lid which is indicated long before it is mature. The epidermal cells where the open- ing is to occur grow less actively than their neighbours, and thus a groove is formed which is the first indication of the oper- culum. The cells at the bottom of the groove have thinner walls than the other cells of the capsule wall, and when it ripens these dry up and are very readily broken, so that the oper- culum is very easily sep- arated from the dry cap- sule. Stomata, according to Schimper, always are present, sometimes in great numbers; but Hab- erlandt ((4), p. 475 )> states that these are al- ways rudimentary, and he regards them as re- duced forms. No seta is formed, but its place is taken physiologically by the upper part of the axis of the archegonial branch, which grows Up beyond the perichaetium, carrying the ripe sporogonium at its top (Fig. 91, E). The upper part of this ''pseu- dopodium" is much en- larged, and a section through it shows the bulbous foot of the capsule occupying nearly the whole space inside it. The ripe capsule breaks through the overlying calyptra, the upper part of which is carried up somewhat as in the higher Mosses, while the basal part together with the upper part of the pseudopodium forms the 'Vaginula." The disorganised contents of the canal cells, which are usually ejected from the archegonium, in Sphagnum remain in a large measure in the central cavity, and on removing the Fig. 93. — Median longitudinal section of a nearly ripe sporogonium of S. acutifoli- urn, X24; ps, pseudopodium; sp, spores; col, columella (after Waldner). V. MOSSES (MUSCI): SPHAGNALES—ANDREJEALES i8i young embryo from the venter of the archegonium, this muci- laginous mass adheres to it and forms a more or less complete envelope about it, in which are often found the remains of spermatozoids. The species of Sphagmim are either monoecious or dirjecious, but in no cases do archegonia and antheridia ocair upon the same branch. The Andre^ales The second order of the Mosses includes only the small genus Andrecoa, rock-inhabiting Mosses of small size and dark A. Fig. 94. — AndrecPa petrophila. A, Plant with ripe sporogonium, Xio; B, median sec- tion of nearly ripe capsule, X8o; ps, pseudopodium; coi, columella. brown or blackish colour. In structure they are intermediate in several respects between the Sphagnales and the Bryales, as has been shown by the researches of Kiihn (i), and W'ald- ner (2), to whom we owe our knowledge of the life-history of Andrecea. They all grow in dense tufts upon silicious rocks, i82 MOSSES AND FERNS chap. and are at once distinguished from other Mosses by the dehis- cence of their small capsules. These, like those of Sphagnum, are raised upon a pseudopodium, and are destitute of a true seta. The capsule opens by four vertical slits, which do not, however, extend entirely to the summit (Fig. 94). This peculiar form of dehiscence recalls the Jungermanniacese, but is probably only an accidental resemblance. The closely-set stems branch freely; the leaves, with three-eighth divergence, are either with a midrib (A. riipestris) or without one {A, petrophila). The growth of the stem is from a pyramidal apical cell, as in Sphagnum, and probably the origin of the branches is also the same as in that genus. The growth of the young leaves is usually from a two-sided apical cell, but another type of growth is found where the apical cell is nearly semicircular in outline, and segments are cut off from the base only. These two forms of apical growth apparently alternate in some instances in the same leaf. The originally thin walls of the leaf cells later be- come thick and dark-coloured, whence the characteristic dark colour of the plant. The stem in cross-section shows an almost uniform struc- ture, and no trace of'the central conducting tissue of the higher Mosses can be found. The outer cells are somewhat thicker- walled and darker-coloured, but otherwise not different from the central ones. Numerous rhizoids of a peculiar structure grow from the basal part of the stem, and from these, new branches arise, which replace the older ones as they die away. These rhizoids are not simple rows of cells as in the Bryales, but are either cylindrical masses of cells or flattened plates. They penetrate into the crevices of the rocks, or apply them- selves very closely to the surface, so that the plants adhere tenaciously to the substratum (Ruhland (2)). Spores and Protonema The germination of the spores and the development of the protonema show numerous peculiarities. The spores may germinate within a week, or sometimes remain unchanged for months. They have a thick dark-brown exospore and contain, chlorophyll and oil. The first rdivisions take place before the- exospore is ruptured, and may §€ in thrfie planes, so that the V. MOSSES (MUSCI): SPHAGNALES—ANDRE^ALES 183 young protonema then has the form of a globular cell mass (Fig. 95, A). This stage recalls the corresponding one in many of the thallose Hepaticae, e. g., Pellia, Rachila, and is entirely different from the direct formation of the filamentous protonema of most Mosses. Some of the superficial cells of this primary tubercle grow out into slender filaments, either with straight or oblique septa, and these later ramify exten- sively. Where there are crevices in the rock, some of these branches grow into them as colourless rhizoids. but, as in the Bryales, there is no real morphological distinction between rhizoid and protonema. Most of the filamentous protonema! branches do not remain in this condition, but become trans- formed into cell plates or cylindrical cell masses, like the stem- FiG. 95. — A, B, Germinating spores of A. petrophila, X200; C, protonema with bud (fe); D, young archegonium in optical section; E, i, 2, two views of a very young embryo of A. crassinerva, X266; F, somewhat older embryo of A. petrophila; G, older embryo showing the first archesporial cells; H, I, cross-sections of young embryos, X200. A-D, after Kuhn; E-I, after Waldner. rhizoids. The flat protonema recalls strongly that of Sphag- num, and is probably genetically connected with it. All of the different protonemal forms, except what Kiihn calls the ''leaf- like structures," vertical cell surfaces of definite form, can give rise to the leafy axes. The development of these seems to cor- respond exactly with that of the other Mosses, and will not be further considered here. i84 MOSSES AND FERNS chap. The Sexual Organs The species of Andrecea may be either moncecious or dioe- cious. Archegonia and antheridia occur on separate branches, but their origin and arrangement are identical. The first- formed antheridium develops directly from the apical cell of the shoot, and the next older ones from its last-formed segments, but beyond this no regularity can be made out. In the first one the apical cell projects, and its outer part is separated from the pointed inner part by a transverse wall. This is followed by a second wall parallel to the first, so that the antheridium rudi- ment is composed of three cells. Of these the lower one takes little part in the future development. Of the two upper cells the terminal one becomes the body of the antheridium, the other the stalk. In the former, by two inclined walls, a two-sided apical cell is developed, and the subsequent growth is the same as in the Bryales. The middle cell of the antheridium rudi- ment divides repeatedly by alternating transverse and longi- tudinal walls, and forms the long two-rowed stalk of the mature antheridium. On comparing the antheridium with that of the other Mosses, we find that it approaches Sphagnum in the long stalk, but in its origin and the growth of the antheridium itself, it resembles closely the higher Mosses. The first archegonium also is derived immediately from the apical cell of the female branch, and the first divisions are the same as in the first antheridium. Here, too, the subsequent development corresponds exactly with that of the higher Mosses, and will be passed over. The ripe archegonium shows no noteworthy peculiarities, and closely resembles in all respects that of the other Mosses. The Sporophyte The more recent researches of Waldner (2) on the develop- ment of the sporogonium of Andrecea have shown clearly that in this respect also the latter stands between the Sphagnacese and the Bryales. The first division in the fertilised ovum is transverse and divides it into two nearly equal parts. The lower of these divides irregularly and much more slowly than the upper one. In the latter (Fig. 95, E), the first division wall is inclined, and is followed by a second one which meets it nearly at right angles, and by walls inclined alternately right V. MOSSES (MUSCI): SPHAGN ALES— ANDRE JEALES 185 • and left — in short, has the character of the famiHar *'two-sIded" apical cell. The number of segments thus formed ranges from eleven to thirteen. Each segment is first divided by a vertical median wall into equal parts, so that a cross-section of the young embryo at this stage shows four equal quadrant cells. The next divisions correspond to those in Sphagnum, and result in the separation of the endothecium and amphithecium. The formation of the archesporium, however, differs from Sphag- num, and is entirely similar to that of the higher Mosses. In- stead of arising from the amphithecium as in the former, the archesporium is formed by the separation of a single layer of cells from the outside of the endothecium. All of the segments do not form spores, but only three or four, beginning wnth the third from the base. The two primary segments of the upper part of the embryo, like the corresponding ones in Sphagnum, go to form the foot, which is not so well developed, however, as in the latter. The originally one-layered archesporium later becomes double, and as in Sphagnum extends completely over the columella, which is thus not continuous with the tissue of the upper part of the sporogonium. As in Sphagnum also, no trace of the intercellular space formed in the amphithecium of the Bryales can be detected. A section of the nearly ripe cap- sule shows the club-shaped columella extending nearly to the top of the cavity. With the growth of the capsule the space between the inner and outer spore-sacs becomes very large to accommodate the growth of the numerous spores. The pseu- dopodium is exactly the same as in Sphagnum, and the vaginula and calyptra are present. The latter is much firmer than in Sphagnum, and like that of the Bryales. Archidium The genus Archidium is one whose systematic position has been long a subject of controversy. It has usually been associ- ated with the so-called cleistocarpous Bryales, but the researches of Leitgeb (8) seem to point to a nearer affinity wuth Andrecca, The species of Archidium are small Mosses growing on the earth, and especially characterised by the small number, but very large size, of the spores contained in the sessile globular sporogonium. Hofmeister ( ( i ) , p. 160), was the first to study the development, and his account agrees in the main with Leit- i86 MOSSES AND FERNS CHAP. geb's, except as to the relation of the columella and outer spore- sac. The first divisions in the embryo correspond exactly to those in Andrecua and the Bryales, and for a time the young embryo grows from a two-sided apical cell. The secondary divisions in the segments, however, are quite different from that observed in any other Moss, and are like those in the anther- idium. Instead of the first wall dividing the segment into equal parts, it divides it very unequally. The second wall strikes this so as to enclose a central cell, triangular in cross- FiG. 96. — Archidium Ravenelii. A, Median section through a nearly ripe sporogonium, X90; B, base of the sporogonium, X27o. section, which with the corresponding cell of the adjacent seg- ment forms a square. This square, the endothecium, does not therefore at first show the characteristic four-celled stage found in all other Mosses. The amphithecium becomes ultimately three-layered, and between the second and third layers an inter- cellular space is formed, as in the Bryales, but this extends com- pletely over the top of the columella. The most remarkable feature, however, is that no archesporium is differentiated, but any cell of the endothecium may apparently become a spore V. MOSSES (MUSCI): SPIIAGMALES—ANDRnjEALES 187 mother cell. The number of the latter is very small, seldom exceeding five or six. They become rounded off, and gradu- ally displace the other endothecial cells, which doubtless serve as a sort of tapetum for the nourishment of the growing spores. Each spore mother cell as usual gives rise to four spores, which are very much larger than in any other Moss. A section of the ripe sporogonium (Fig. 96), shows that only one of the primary three layers of amphithecial cells can be recognised except at the extreme apex and base. No seta is present, and a foot much like that of Andrecea, and penetrating into the tis- sue of the stem apex, is seen. Leitgeb is inclined to look upon Archidinm as a primitive form allied on the one hand to Andrecca and on the other to the Hepatic^, possibly Notothylas. However, as his assump- tion that the latter has no primary columella has been shown to be erroneous, his comparison of the w-hole endothecium of Ar- chidiuni wath that of Notothylas cannot be maintained, as we have shown that in the latter, as in Anthoceros, the arche- sporium arises from the amphithecium, and not from the en- dothecium, as is the case in Archidinm. Inasmuch as the game- tophyte and sexual organs of Archidinm are those of the typical Mosses, it seems quite as likely that the older view that Ar- chidium is a degenerate form is correct. At any rate, until more convincing evidence can be brought forward in support of a direct connection between it and the Hepaticae than the formation of the spores directly from the central tissue of the sporogonium, it cannot be said that the question of its real affin- ities is settled. CHAPTER VI THE BRYALES Under the name Bryales may be included all the other Mosses ; for. although the so-called cleistocarpous forms are sometimes separated from the stegocarpous Mosses as a special order, the Phascacese, the exact correspondence in the development of both the gametophyte and sporophyte shows that the two groups are most closely allied, the former being either rudimentary or degraded forms of the others. With few exceptions the protonema is filamentous and shows branches of two kinds, the ordinary green ones with straight transverse septa, and the brown-walled rhizoids with strongly oblique ones, but the two forms merge insensibly into one another, and are mutually convertible. In a few forms, notably the genus Tetraphis, the protonema is thalloid, and as in Sphagnum these flat thalli give rise to filamentous proto- nemal threads, which in turn may produce secondary thalloid protonemata. The genus Diphyschim (C. Muller (3), pp. 169, 170), develops upon the protonema solid, trumpet-shaped bodies. In some of the simpler forms, e. g., Ephemerum, the protonema is permanent, and the leafy buds appear as append- ages of it ; but in most of the larger Mosses the primary proto- nema only lives long enough to produce the first leafy axes, which later give rise to others by branching, or else by second- ary protonemal filaments growing from the basal rhizoids. The early stages of development of the primary protonema are easily traced, as the spores of most Mosses germinate readily when placed upon a moist substratum. The ripe spores usually contain abundant chlorophyll and oil, and the thin exospore is brown in colour. The spore absorbs water and begins to en- large until the exospore is burst, when the endospore protrudes 188 CH. VI. THE BRYALES 189 as a papilla which grows out into a filament ; or the endospore sometimes grows out in two directions, and one of the papillcC remains nearly destitute of chlorophyll and forms the first rhi- zoid. The growth of the protonemal filaments is strictly apical, no intercalary divisions taking place except those by which lateral branches arise. If abundant moisture is present, the protonema grows with great rapidity and may form a dense branching alga-like growth of considerable extent. Sooner or later upon this arise the leafy gametophores. The develop- ment of the latter, as we have seen, also takes place abundantly gam.. — Fig. 97. — Funaria hygrometrica. A, Fragment of a protonemal branch with a young gametophoric bud; r, rhizoid; B, median optical section of the bud; C, older bud — • I, surface view; 2, optical section; x, apical cell; D, protonema with a still older gametophore (^gam) attached. A-C, X225; D, X36. from the secondary protonemal filaments which may be made to grow from almost any part of the gametophore. The development of the bud is as follows. From a cell of the protonema a protuberance grows out near the upper end. This is at first not distinguishable from a young protonemal branch, but it very soon becomes somewhat pear-shaped, and instead of elongating and dividing simply by transverse walls, the division walls intersect so as to transform it into a cell mass. 190 MOSSES AND FERNS chap. After the cell is separated it is usually divided at once by a strongly oblique wall, which is then intersected by two others successively formed and meeting each other and the first- formed one at nearly equal angles, so that the terminal cell of the young bud (Fig. 97, A), has the form of an inverted pyramid; that is, by the first divisions in the bud the characteristic tetrahedral apical cell of the gametophore is established. From now on the apical cell divides with perfect regularity, cutting off three sets of lateral segments. From the base of the young gameto- phore the first rhizoid (Fig. 97, A, r ), is formed at a very early period. The first two or three segments do not give rise to leaves, and the leaves formed from the next younger segments remain imperfect. Thus in Funaria hygrometrica these earliest formed leaves show no midrib. The young leaves rapidly elongate and completely cover up the growing point of the young bud, and are at first closely imbricated. Later, by the elongation of the axis, the leaves become more or less completely separated (Fig. 97, C, D). In Funaria, as well as in many other Mosses, buds are often met with that have become arrested in their development, lost their chlorophyll, and assumed a dark- brown colour. This arrest often seems to be the result of un- favourable conditions of growth, and under proper conditions these buds probably always will develop either directly or by the formation of a secondary protonema into perfect plants. Apical Growth of the Stem The growth of the stem of the fully-developed gametophore is better studied in one of the larger Mosses. The growth of the gametophore is so limited in length in Funaria that it is not so well adapted for this. Perhaps the best species for this purpose is the well-known Fontinalis antipyretica, which has already been carefully studied by Leitgeb ( i ) . Amhlystegium riparium, var. Uuitans, was examined by me and differed in some points from Leitgeb' s figures of Fontinalis. Fig. 98, A shows an exactly median longitudinal section through a strong growing point. Compared with Leitgeb's figures the apical cell is much deeper than in Fontinalis, and in consequence the young- segments more nearly vertical. Here, as in Sphagnum, the first wall in the young segment divides it into an inner and an outer cell, from the latter of which alone are formed the lateral VI. THE BRYALES 191 appendages of the stem. The inner cells of the segments by repeated longitudinal and transverse divisions form all the tis- sues of the axis. The second division wall in the segment, like that in Sphagnum, is at right angles to the first, but in Ambly- stcgmm it extends the whole breadth of the segment. By this division the outer of the two primary cells of the segment is divided into an upper cell, from which the leaf develops, and a lower one from which the outer part of the stem and the burls are formed. The leaves grow from a two-sided apical cell Fig. 98. — Amblystegium riparium, var. fluitans. A, IMedian longitudinal section of a strong shoot; x, apical cell; x', initial of a lateral branch, X250; B, transverse section through the apex, X250; C, similar section through a young branch, Xsoo* (Fig. 99), as indeed they seem to do in all Mosses, and the divisions proceed w^ith great rapidity and the young leaves quickly grow beyond and surround the growing point. In Amblystegiiun, as in all the typical Bryalcs, the leaf has a well- developed midrib. The formation of this begins while the leaf is very young and proceeds from the base. In the middle row of cells (Fig. 99, C), a w^all first arises parallel to the surface of the leaf, and this is follow^ed by a wall in the cell on the lower side of the leaf (Fig. 99, D). By further divisions in all the 192 MOSSES AND FERNS CHAP. cells of this central strand the broad midrib found in the mature leaf is developed. In Amhlystegiwn all the cells of the midrib are, alike and have thickened walls. The midrib projects on both sides of the leaf, but rather more strongly upon the lower side. In Funaria (Fig. loo), the structure of the midrib Is more definite. Here two rows of cells take part in the formation of the midrib. Each of these first divides as in Amblystegium by a wall parallel to the surface of the leaf, so that in cross-section the central part of the leaf shows a group of four cells, those Fig. gg.— 'Amblystegium riparium, var. fiuitans. A, Longitudinal section of the stem passing through a young lateral branch {k) ; h, hair at the base of the subtending leaf; B, horizontal sec+^^ion of a very young leaf, showing the apical cell (,x) ; C, D, transverse sections of young leaves, showing the development of the midrib. All the figures X525. on the outer side being larger than the others. In the former the next wall is a periclinal one and divides the cell into an inner and an outer one. From the two inner cells by further division is formed the group of small conducting cells that traverse the centre of the midrib, while the outside cells together with those on the inner side of the midrib become much thickened and serve for strengthening the leaf. As in Amblystegium the lamina of the leaf remains single-layered, and its cells contain numerous large chloroplasts which, as is well-known, continue VI. THE BR VALES 193 to multiply by division after the cells are fully f^rown. The marginal cells in the leaf of Funoria are much narrower than those between them and the midrib, and their forward ends Fig. 100. — Funaria hysrometrica. A, Transverse section of the apex of a young shoot, X515; B, C, cross-sections of young leaves, X515; D, cross-section of the stem, X257. often project somewhat, giving the margin of the leaf a serrate outline, which is also common in many other Mosses. The Branches For the study of the branching of the stem, Amhlystcgunn again is much better than Funaria, wdiose short stem and infre- quent branching makes it difficult to find the different stages. In Amblystegiuiu, however, every median section will show some of the stages, and it is easy to follow out all the details, as has already been done in Fontinalis by Leitgeb. The lateral shoot originates from a basal cell of the segment below the middle of the leaf. It is very easily seen that it belongs to the 13 194 MOSSES AND FERNS chap. same segment as the leaf standing above it, and therefore is not axillary in its origin. The mother cell of the young branch projects above the surrounding cells, and in it are formed in succession three oblique intersecting walls which enclose the narrow pyramidal apical cell (Figs. 98, 99). The secondary divisions in the first set of segments are not so regular as in the later ones, but the bud rapidly grows, and very soon the perfectly regular divisions of the young segments are estab- lished. So far as investigations have been made upon other genera, they follow the same line of development as Ambly- stegium, Fontinalis, and Sphagnum. Where the growth of the main axis is stopped by the form- ation of sexual organs, a lateral branch frequently grows out beyond the apex of the main axis, as in Sphagnum, and thus sympodia arise. In other cases, where the growth of the lat- eral branches is limited, characteristic branch systems arise, such as we find in Thuidium or Climacium (Fig. 86). Compared with Amhlystegium, the growing point of Funaria and other Mosses of similar habit is much broader, and the apical cell not so deep. The arrangement of the segments is much the same, except that the original three- ranked arrangement of the segments which is retained in Fonti- nalis^ is replaced in most Mosses by a larger divergence, owing to a displacement like that in Sphagnum. A cross-section of the older stem (Fig. 100, D), shows in most Bryales a central cylinder of small thin-walled cells sur- rounded by a large-celled cortical tissue, which in the older parts of the stem often has its walls strongly thickened and reddish brown in colour. An epidermis, clearly recognisable as such, cannot usually be detected. The outer cells contain chlorophyll, which is wanting in the central cylinder. The rhizoids in Funaria grow mainly from the base of the stem, and the first ones arise very soon after the young bud is formed. Their growth, like that of the protonemal branches, is strictly apical, and they branch extensively. The young ones are colourless, but as they grow older the walls assume a deep brown colour. Usually the division walls in the rhizoids are strongly oblique. Their contents include more or less oil, and where they are exposed to the light, chlorophyll. ^ This is only strictly true in the smaller branches. VI. THE BRYALES The Sexual Organs 195 Funaria is strictly dioecious. The male plants (Fig. loi, A) are easily distinguished by their form. They are about I cm. in height, with the lower leaves scattered, but the upper «3 r T rt ■' P" c .a c .s c .t; ^> u « .2 C bo s o >> 9, •- , ° "St" ^ .^ >^^# .2 '^ *> •" _r O C t3 K C3 « a o B »4 cd o ones crowded so as to present much the appearance of a flower whose centre forms a small reddish disc. These male plants either grow separately or more or less mixed with the females. 196 MOSSES AND FERNS ciiw. Whether the first antheridium, as in Andrecea and Fontinalis, arises from the apical cell is doubtful, and it is impossible to trace any regularity in the order of formation of the very numerous antheridia. Except in old plants, all stages of de- velopment are found together, and the history of the anther- idium may be easily followed. A superficial cell projects above its neighbours, and this papilla is cut off by a transverse wall. Fig. 102. — Funaria hygrometrica. Development of the antheridium. A-D, Longitudinal sections of young stages, X600; D is cut in a plane at right angles to C; E, optical section of an older stage, X300; G, F, cross-sections of young antheridia, X600; H, diagram showing the first divisions in the antheridium; I, young spermatozoids, X1200. The outer cell either becomes at once the mother cell of the antheridium, or other transverse walls may occur, so that a short pedicel is first formed (Fig. 102, A). Finally in the terminal cell, as in Andrecea, two intersecting walls are formed' enclosing a two-sided apical cell, from which two ranks of seg- ments are cut off in regular succession (Figs. A, B, C). The number of these segments is limited, in Funaria not often ex- ceeding seven, and after the full number has been formed, the VI. THE BRYALES 197 apical cell is divided by a septum parallel with its outer face into an inner cell, which with the inner cells ni the se<(nients forms the mass of sperm cells, and an outer cell which prc^luces the upper part of the wall. Before the full number is com- pleted, the secondary divisions begin, ])roceeding from the base upward. These are very regular, and correspond closely to those in the antheridium of the Jungermanniaceae, and can only be clearly made out by comparing transverse and vertical sec- tions of the young antheridium. Fig. 102, H, shows a diagram illustrating this : i is the wall separating two adjacent seg- ments, and 2 the first wall formed in the segment itself. The wall 2, it will be seen, starts near the middle of the periphery of the segment and strikes the wall i far to one side of the centre, so that the segment is thus divided into two cells of very unequal size, although their peripheral extent is nearly equal. The next wall (3) strikes both the w^all i and 2 at about equal distances from the periphery, and thus each segment is divided into an inner cell wdiich in cross-section has the form of a tri- angle, and two peripheral cells. The latter divide only by radial walls, and give rise to the single-layered wall of the antheridium. The inner cells of the segments by further di- vision in all directions form the mass of sperm cells. The first division w^all in the central cell starts from near the middle of the segment wall and curves slightly, so that the two resulting cells are unequal in size. From this first division wall usually two others having a similar form extend to the peripheral cells, and these are next followed by others nearly at right angles to them. After this transverse and longitudinal walls succeed with such regularity that the limits of the primary segments remain perfectly evident until the antheridium is nearly full grown. The central cells in the fresh antheridium are strongly re- fringent and in stained sections show^ a much more granular consistence than the outer ones. The nucleus, as in other cases studied, loses its nucleolus before the formation of the sperma- tozoids begins. The latter in their structure and development correspond with those of Sphagnum, but owing to their smaller size are not favourable for studying the minute details of de- velopment. In the peripheral cells are numerous chloroplasts which in the ripe antheridiu.m lie close to the inner w^all of the cell As 198 MOSSES AND FERNS CHAP. the antheridium ripens, these gradually assume a bright orange- red colour. The development of the stalk varies in different cases. Sometimes it consists of a row of several cells, some- times the antheridium is almost sessile. The lowermost seg- B. li Fig. 103. — Funaria hygrometrica. A, Antheridium that has just discharged the mass of sperm cells (B), X300; C, spermatozoids, X1300; D, paraphysis, X300; E, male "flower" of Atrichum undulatum, X6. ments of the apical cell help to form the upper part of the stalk, and sometimes the two lowest seem to take no part in the formation of the sperm cells. There is no absolute uniformity in the cell divisions of the stalk, which varies in the arrange-;; VI. THE BRYALES igg ment of the cells in different individuals in the same inflor- escence. The ripe antheridium opens promptly when placed in water. At the apex there is usually ])resent a single cell decidedly larger than its neighbours (Fig. 103, A), or sometimes there are two opercular cells (Goebel (22), p. 239). All of the parietal cells become strongly turgescent and this is especially the case in the terminal cell, which finally bursts and forms a narrow opening through which the mass of sperm-cells is forced out by the pressure of the distended parietal cells, and the swell- ing of the mucilage derived from the disintegration of the walls of the sperm-cells. The opercular cell in Punaria is not de- stroyed, as a rule, and is still very conspicuous after the sperm- cells have been discharged, so that the empty antheridium, ex- cept for a slight contraction of its lower part, looks very much as it did before the escape of the sperm-cells. In some other Mosses, e. g., Polytrichum, Catharinia, the opercular cap con- sists of several cells (Goebel, 1. c). The whole mass of sperm- cells is thrown out without separating the cells, and in this stage the walls of the sperm-cells are still very evident. It sometimes happens that the mass is thrown out before the spermatozoids are complete, in w^hich case they never escape. If, however, the spermatozoids are mature, they show active motion within the sperm-cells while these are still in connection, and are set free by the gradual dissolution of the mucilaginous walls. The free spermatozoid is much like that of Sphagnum, but the body is somewhat shorter. The cilia are relatively very long and thick, and as in all Bryophytes but two in num- ber. A small vesicle can usually be seen attached to the pos- terior end. Growing among the antheridia are found peculiar sterile hairs, or paraphyses. These in Funaria are very conspicuous, and, consist of a row of cells tapering to the base, and very much larger at the apex. The terminal cell, or sometimes two or three of them, are almost globular in form and very much distended. All the cells of the paraphyses contain large chloroplasts, which in the globular end cells are especially con- spicuous and are often elongated with pointed ends. The archegonia are formed while the female plant is still very small, and it Is much more difficult to recognise the female plants than the males. The archegonia are ripe at a time when 20Q MOSSES AND FERNS CHAP. the female plant is still but a few millimetres in height. In this case there is no doubt that the apical cell forms an archegoniuni directly, but not necessarily the first one, which arises usually from one of the last- formed segments. The elongation of the axis of the female branch is but slight, even in the later stages, Fig. 104.— Longitudinal section through the apex of a male plant of F. hygrometrica, X300; L, leaf; (^, antheridia; p, paraphyses. and the plant remains bud-like even after the sporogonium is) developed. In regard to the development of the leafy axis, ob gametophore, therefore, Funaria offers a very marked contrast?, to Fontinalis or Sphagnum, where the gametophore reaches such a large size and has practically unlimited growth. The young archegonia are quite colourless, and the details; VI. THE BRYALES 201 of their structure may ])e made out without difficulty. The first division separates a basal cell from a terminal cell, which is the mother cell of the archegonium. In the latter three walls now arise, as in tlic Hepaticse and Andrecra, but in Fiinaria these do not all reach to the basal wall, but intersect at some distance above it, so that they enclose a tetrahedral cell, pointed 202 MOSSES AND FERNS chap. below instead of truncate. The tetrahedral cell now divides by a transverse wall into an upper cell, corresponding to the ''cover cell" of the Liverwort archegonium, and an inner one (Fig. 105, A), which gives rise to the primary neck canal cell, the egg, and the ventral canal cell. From this point, however, the development proceeds in another way, and follows the course observed in Andrecea. The cover cell, instead of divid- ing by quadrant walls, has a regular series of segments cut off from it, and acts as an apical cell. These segments are cut off parallel both to its lateral faces and base, and thus form four rows of segments, the three derived from the lateral faces forming the outer neck cells, and the row of segments cut oft' from the base constituting the axial row of neck canal cells. Each row of lateral segments is divided by vertical walls, and forms six row^s, w^hich later divide by transverse walls as well so that the number of cells in each row exceeds the original number of segments. This is not the case with the canal cells, which, so far as could be determined, do not divide after they are first formed. The wall of the venter owes its origin en- tirely to the three peripheral cells formed by the other primary walls in the archegonium mother cell. This becomes two-lay- ered before the archegonium is mature, and is merged gradu- ally into the massive pedicel, which in the Mosses generally is much more developed than in the Hepaticse. In the older archegonia the neck ceJls, do not stand in vertical rows, but are somewhat obliquely placed, owing to a torsion of the neck dur- ing its elongation. From the central cell the ventral cia'nal cell is cut off, as usual, but is relatively smaller than is usual among the Hepaticse. The egg shows a distinct receptive spot, which is not, however, very large. The rest of the egg shows a densely granular appearance, and the moderately large nucleus shows very little colourable contents, beyond the large central nucleolus. The terminal cells of the open archegonium diverge widely, giving the neck of the archegonium a trumpet shape (Fig. 105, F). Usually some of the cells become detached and are thrown off. Holferty ( i ) has made a careful study of the archegonium in Mnium cuspidaHim and finds that the archegonium in its earliest stages grows from a two-sided initial cell like that of the antheridium. This is later replaced by the usual tetra- hedral apical cell found in other species. After a more or less VI. THE BRYALES 203 massive pedicel is formed, the apical cell divides, as in fnnaria, into an inner and an outer cell. The former, as usual, ^ives rise to the central cell, from which later arise the egg" and ven- tral canal cell, and a second cell, which is the primary neck canal cell. The latter, according to Ilolferty, undergoes fur- ther divisions and the secondary canal cells, cut off from the base of the apical cell, also undergo further divisions. There may be as many as ten neck canal cells finally developed. Holferty also describes and figures several abnormal struc- tures, intermediate in character between the archegonium and antheridium. While in Fnnaria and Polytrichnm the plants are regularly dioecious, in many Mosses this is not the case. Both antheridia and archegonia may occur in the same "inflorescence," or they may be in separate groups upon different parts of the same plant. Some doubt has been thrown upon the nature of the so- called hermaphrodite inflorescences, and it is possible that they are really composed of distinct but closely approximated inflor- escences. (Satter (2) ; 'see Ruhland (i), pp. 204, 205.) The Sporophyte The first (basal) w^all in the fertilised ovum divides it into an upper and low^er cell, as in Sphagmmi and Andrecca, and the next divisions correspond closely to those in the latter. In both cells a wall is formed intersecting the basal wall, but not at right angles. This is especially the case in the upper cell where a second wall strikes the first one nearly at right angles, and establishes the two-sided apical cell by which the embryo grows for a long time. In the lower cell the divisions are somewhat less regular, but here also it is not uncommon to find a some- what similar state of affairs, so that the embryo may be said to have two growing points, although the lower end shows neither such regular nor so active growth as the upper one. In the lat- ter the divisions follow each other with almost mathematical precision. There seems to be no rule as to how many segments are cut off from the apical cell before it ceases to function as such, but there are more than in Andrecca, and the embryo soon becomes extremely elongated. A series of transverse sections of the young sporogonium shows very beautifully the succession of the first walls in the young segments. In a sec- tion just below the apex (Fig. 107, A), each segment is seen to 204 MOSSES AND FERNS CHAP. .■ ( .: -. . Fig. io6. — Funaria hys:rometrica. Development of the embryo. A, Optical section of a very young embryo; B, C, surface view and optical section of an older one, X6oo; C, D, longitudinal sections of the apex of older embryos, X6oo; en, endo- thecium; am, amphithecium. VI. THE BRYALES 205 be first divided by a median wall into two equal cells. In Fiinaria usually the next division wall is periclinal, and at once separates endothecium and amphithecium. In most other Bryineae that have been examined, however, and this may also occur in Fimaria (see Fig. 107, A), the second walls formed in the young segments are anticlinal, and it is not until the third set of walls is formed that the separation of endothecium and amphithecium is complete. The next divisions (Fig. 107, C), are in the amphithecium, and separate it into two layers. In the endothecium a series of walls is next formed, almost exactly repeating the first divisions in the original segment (Figs. D, N Fig. 107. — Five transverse sections of a young embryo of F. hygrometrica. A, Just below the apex, the others successively lower down; en, endothecium, X450' . E), and transforming it into a group of four central cells and eight peripheral ones. Each of the latter divides twice by in- tersecting walls, so that a group of about sixteen cells (Fig. 108, A), occupies the middle of the endothecium. The eight peripheral cells divide by radial walls, after which each of these cells is divided by a periclinal wall into an outer and an inner cell (Fig. 108, B), and the outer cells divide rapidly by radial walls and form the archesporium. The single layer of cells immediately within, and therefore sister cells of the primary archesporial ones, is the inner spore-sac. The account of the development of the endothecium here given differs slightly from the account of Kienitz-Gerloff (2), 206 MOSSES AND FERNS CHAP. It was found first that there was not the absolute constancy in the number of cells given by him; thus in Fig. io8, A there are only fourteen cells in the inner part of the endothecium, and although there are sixteen cells in the outer row their position is not perfectly symmetrical. Again the periclinal division of the cells of the inner spore-sac takes place later than he states is the case. In the eight primary cells of the amphithecium there first arise periclinal walls that divide each cell into an inner small cell in contact with the endothecium, and an outer larger one. Fig. 108.— Three transverse sections of an older sporogonium of F, h^grometrica, X400; ar, archesporium; t, intercellular spaces. This first division separates the wall of the capsule from the outer spore-sac. The latter next divides by radial and trans- verse walls, and later by periclinal walls into two layers (Fig. 108). Almost coincident with the latter, the rows of cells lying immediately outside it show a very characteristic appear- ance. They cease to divide, and with the rapid growth in diameter of the capsule become much extended both vertically and laterally, but are compressed radially. It is between these cells and the spore-sac that the characteristic air-space found in the capsule is formed. This is first evident shortly after the enlargement of the base of the capsule begins. The devel- VI. THE BRYALES 207 opment can be very easily followed in longitndinal sections made at this stage. The formation of the space begins at the base of the capsule and proceeds toward the top. Hie line of cells bordering on the spore-sac is very easily followed, owing to their being so much larger than the neighlxjuring ones. As this is followed down, it is found that at the base of the capsule the cells are separated by large intercellular spaces, which be- come less marked toward the apex. With the rapid enlarge- ment of the capsule these spaces become very large, and sec- tions made a little later show that during this process the cells remain in contact at certain points, and form short filaments that extend across the space and unite the wall of the capsule with the outer spore-sac. At the base of the capsule the for- mation of intercellular spaces is not confined to the single layer of cells but involves the whole central mass of tissue, which be- comes thus transformed into a bundle of filaments connecting the columella with the basal part (apophysis) of the capsule. The innermost of the two layers of cells between the arche- sporium and the air-space finally undergoes a second periclinal division, and in the full-grown sporogonium the archesporium is bounded on the outside by three layers of cells. The differentiation into seta and capsule takes place late in Fimaria, and the first indication of this is the enlargement of a zone between the two, forming the apophysis, which at this stage (Fig. 109), is much greater in diameter than the upper part of the capsule. Sections through the apophysis and seta show a less regular arrangement of the cells than in the sporiferous part of the capsule, but the general order of cell-succession is the same, except for the formation of the archesporium. Almost as soon as the capsule is recognisable, the first indication of the operculum or lid becomes evident. About half-way between the extreme apex of the sporogonium and the top of the apophysis, a shallow^ depression is noticed extending completely round the capsule and separating the sharply conical apex from the part below. An examination of a longitudinal section at this point shows that at the point of separation the epidermal cells of the opercular portion are much narrower than those immediately below. Examining the tis- sues farther in, the archesporium is seen to extend only to a point opposite the base of the operculum, and the same is true of the row of large cells where the air-space is formed. If a Fig. 109. — Funaria hygrometrica. A, Longitudinal section of a sporogonium showing the first differentiation of its parts, X about 96; B, the upper part of the same, X600; r marks the limits of the theca and operculum; C, basal part of the cap- sule of the same, X600. The intercellular spaces are beginning to form; ar, archesporium; col, columella. VI. THE BRYALES 200 similar section is made through an older capsule (Fig. no), it is evident at once that the enlargement takes place mainly below the junction of the operculum, and there is also a similar but less pronounced increase in diameter in the operculum itself ; but there is a narrow zone at the junction of the operculum and capsule, where the epidermal cells increase but little in depth, while those above this point become very much larger and pro- ject beyond them. This narrow zone of cells marks the point where when ripe the operculum becomes detached. The latter, Fig. ho. — Longitudinal section of an older capsule of F. hygrometrica; i, intercellular spaces; sp, archesporium; r, cells between operculum and theca, XS^S- Up to the time the sporogonium is ripe, is composed of a close tissue without any intercellular spaces. The epidermal cells, seen from the surface, are seen to be arranged in spiral rows running from the base to the apex. Its central part is made up of large thin-walled parenchyma, continuous with the tissue of the columella. The archesporium, therefore, is not continuous over the top of the columella, as in Sphagnum and Andrecea, but is cylindrical. The archesporium forms simply a single layer of small cells, and occupies a very small part of the sporo- 14 210 MOSSES AND FERNS CHAP. gonium, much less, relatively, than in any of the forms hitherto described. Before the final division of the spores it divides more or less completely into two layers. The cells resulting from this last division are the spore mother cells, which separate soon after their formation and lie free in the space betw^een the inner and outer spore-sacs, where each one divides into four tetrahedral spores. In the operculum, as the capsule approaches maturity, the differentiation of annulus and peristome takes place. The annulus consists of five or six rows of cells that occupy the B Fig. III. — A, Longitudinal sections of a nearly ripe capsule of F. hygrometrica, X260; per, peristome; r, annulus; t, thickened cells forming the margin of the theca; B, the sporogenous cells shortly before the final divisions; i, inner; 0, outer spore- sac, X525- periphery of the broadest part of the operculum. The upper rows of cells are very much compressed vertically, but are greatly extended radially and have their walls thicker than those of the neighbouring cells. These thickened annulus cells form the rim of the loosened operculum. The two lower rows of annulus cells — the annulus proper — have thin walls and finally become extremely turgescent. It is the destruction of these VI. THE BRYALES 211 cells, when the capsule is ripe, that effects the separation be- tween the operculum and theca. The peristome arises from the fifth layer of cells from the outside of the operculum. If a median longitudinal section of a nearly ripe capsule is examined, the row of cells belonging to this layer (Fig. iii, per), is at once seen to have the outer walls strongly thickened, and this thickening extends for a short distance along the transverse walls. The inner walls of the cells also show a slight increase in thickness, but much less marked than the outer ones. A similar thickenhig of the cell walls occurs also in about three rows of cells which run from S. "^- Fig. 112. — Longitudinal section of a fully-developed sporogonium of Funaria hygro- metrica, X about 40; s, seta: a, apophysis; sp, spores; col, columella; r, annulus; o, operculum. the outside of the capsule to the base of the peristome, and form the rim of the ''theca" or urn. The epidermis of the whole capsule has its outer walls very much thickened, and upon the apophysis are found stomata quite similar to those found upon the sporogonium of Antho- ceros or upon the leaves of vascular plants. Haberlandt ( (4), p. 464), showed that while the form of the fully-developed stoma in Funaria differs from that of most vascular plants, this difference is secondary, and that in its earlier stages no difference exists. This can be easily verified, and with little difficulty all the different stages found. The young stoma (Fig. 113), has the division wall extending its whole length. 212 MOSSES AND FERNS CHAP. as is the case in stomata of the ordinary form. As the stoma Fig. 113.— ~Funaria hygrometrica. A, Young; B, older stoma, from the base of the capsule; C, vertical section, X360. grows larger, however, the median wall does not grow as fast as the lateral walls, and a space is left between its extremities, B, A. Fig. 114. — Funaria hygrometrica. A, Part of the peristome; o, an outer tooth; t, one of the inner teeth, X85; B, section of the seta, X260; C, cross-section of upper •part of calyptra, X525, SO that the two guard cells have their cavities thrown into communication, and the division wall forms a cellulose plate vr. THE BRYALES 213 extending from the lower to the upper surface of the stoma, but with its ends quite free. The formation of the pore by the sphtting of the middle lamella of the division wall takes place in the ordinary way. Later the walls of the epidermal cells become very thick and show a distinct striation (Fig. 113). By the formation of the stomata the green assimilat- ing tissue of the apophysis and central part of the capsule is put into direct communication with the external atmosphere. The lower part of the seta grows downward and penetrates the top of the stem of the gametophyte, from which, of course, it derives a portion of its sustenance. The centre of the seta is traversed by a well-marked central cylinder, whose inner cells are small and thin-walled, and are mainly concerned in conducting water ; immediately outside of this is a circle of thick-walled brown cells (leptome of Haberlandt), and the rest of the seta is made up of nearly similar thick-walled cells which grow smaller toward the periphery. At maturity, as the supply of w^ater is cut off from below, the capsule dries up, and all the delicate parenchyma compos- ing the columella and inner part of the operculum, as well as that between the spore-sac and the epidermis of the theca, com- pletely collapses, leaving little except the spores themselves, and the firm cell wells of the peristome, and the cells connecting the latter with the wall of the capsule. By the breaking down of the unthickened lateral and transverse walls of the peri- stomial cells, the outer and inner thickened walls are separated and form the two rows of membranaceous teeth that surround the mouth of the urn^ (Fig. 114). By the drying up of the thin-walled cells between the annulus and the margin of the theca the operculum is loosened and is very easily separated. The teeth of the peristome are extremely hygroscopic, and probably assist in lifting off the operculum as well as removing the spores from the urn. When wet they bend inward, extend- ing into the cavity of the urn. As they dry they straighten out and lift the spores out. The marked hygroscopic move- ments of the seta also are no doubt connected with the dissem- ination of the spores. The calyptra in the Bryales is very large and is carried up on the top of the sporogonium in the form of a conspicuous membranaceous cap. As in other forms it is the venter alone that shows secondary growth. In Fimaria it increases very 214 MOSSES AND FERNS chap. much in diameter at the base, where it is widened out like a bell, and far exceeds in diameter the enclosed embryo. Above it is narrow and lies close to the embryo. After a time the embryo grows more rapidly in length than the calyptra, which then is torn away by a circular rent about its base, and is raised on top of the elongating sporogonium. The lower por- tion remains delicate and nearly colourless, but the upper part has its cells thick-walled and dark-brown in colour (Fig. 114, C). Tipping the whole is the persistent dark-brown neck of the archegonium. Classification of the Bryales CleistocarpcB The simplest of the Bryales are the CleistocarpcB or those in which there is no operculum developed, and in consequence the capsule opens irregularly. If Archidhtm is removed from this group the simplest form known is Ephemerum. In this genus, from a highly-developed filamentous protonema are pro- duced the extremely reduced gametophores. According to Miiller, (2) who has studied the life-history of this genus, both male and female branches arise from the same protonema, and are only distinguishable by the smaller size of the former. The axis of the branch is scarcely at all elongated, and the leaves therefore appear close together. The sexual organs corre- spond closely in origin and structure to the other Bryales. The development of the sporogonium in its early phases is also the same, and the differences only appear at a late stage. The separation of endothecium and amphithecium is apparently ex- actly the same as in other Bryales, and from the former is de- rived the archesporium, which like that of Funaria has the form of a hollow cylinder through which the columella passes. Be- tween, the outer spore-sac and the wall of the sporogonium an intercellular space is also formed, but the separation of the cells is complete, and there are no filaments connecting the spore-sac and the sporogonium wall as in Funaria. The cells of the archesporium are few in number and correspondingly large (Fig 115, E), and before the division into the spores takes place all the central tissue of the columella is absorbed, and the spore mother cells occupy the whole central space, where the division of the spores is completed, and at maturity the VI. THE BRYALES 21 Fig. 115. — A, Longitudinal section of the young sporogonium of Pleuridium subulatum, X8o; B, part of the same, X600; sp, archesporium; C, young embryo of Phasciim cuspidatum, optical section, X17S; D, cross-section of an older embryo of the same, X350; sp, archesporium; E, longitudinal section of the central part of the young sporogonium of Ephemerum pliascoides, X350; sp, archesporium. C, D, after Kienitz-Gerloff ; E, after MuUer. 2l6 MOSSES AND FERNS CHAP. whole of the capsule is filled with the large spores, and no trace of the columella remains. Nanomitrium (Goebel (22), p. 374), closely resembles Ephemerum in the development of the sporophyte. The highest members of the Cleistocarpse, such as Phascum and Pleiiridhim (Fig. 116), approach very closely in structure the stegocarpous Bryales. In these the gametophore is much better developed than in Ephemerum, and the protonema not so conspicuous. The leaves also frequently have a well- developed midrib which is wanting in the leaves of Ephemerum. Kienitz-Gerlofif (2) has carefully studied the embryogeny of Phascum cuspidatum, and except in a few minor details it corresponds verv closely to that of Funaria, except, of course, as re- gards the operculum and peristome, which are absent. In Phascum, however, the archesporium is dif- ferentiated earlier than in Funaria. In each of the four primary cells of the endothecium, as seen in trans- verse section, a periclinal wall arises which at once separates the archesporium from the columella (Fig. 115, D). The outer spore- sac has but two lavers of cells, and the capsule wall three, and between them the large lacuna is formed as in Funaria; but in Phascum as in Ephemerum, the separation of the cells is complete. In the seta a slightly-developed central cylinder of conducting tissue is de- veloped, derived, as in Funaria, from the endothecium, but in Phascum it is much less conspicuous. Pleuridium (Fig. 115, A) in its later stages corresponds exactly to Phascum, ex- cept that the capsule is more slender. In both of these genera the seta remains short, but is perfectly evident. Whether the absence of a distinct operculum in the cleistocarpous Mosses is a primitive condition, or whether they are reduced forms, it is impossible to determine positively from a study of their em- bryogeny. Fig. 116. — Pleuridium suhulatum, X20. VI. THE BRYALES 217 Stegocarpco Very much the larger number of Mosses belong to this group, which is primarily distinguished from the foregoing by the presence of an operculum. Of course among the 7000 or more species belonging here there are many differences in struc- ture ; but these are mainly of minor importance morphologically, and only the more important differences can be considered here. As we have already seen, there is great uniformity in the growth of the stem, which, with the single exception of Fis- sidens, has always a three-sided pyramidal apical cell. In Fissidens this is replaced by a two-sided one, but even here it has been found (Goebel (8), p. 371) that the underground Fig. 117. — Cyathophorum pennatum, showing three rows of leaves; sp, sporophytes, stems have a three-sided initial cell, which is gradually replaced by the two-sided one after the apex of the shoot appears above ground. In Fissidens the leaves are arranged in two rows cor- responding to the two sets of segments, and are sharply folded,, so that the margins of the leaf are covered over by those of the next older ones, leaving only the apex free. A similar arrange- ment is found in the genus Bryoziphion (Enstichia), but here there is a three-sided apical cell, and the two-ranked arrange- ment of the leaves is secondary. In Cyathophorum (Fig. 117), there are two row^s of large dorsal leaves and a row of much 2i8 MOSSES AND FERNS chap. smaller ventral ones, so that the plant resembles very closely a foliose Liverwort. The curious genus Schistostega shows also a two-ranked arrangement of the leaves of the sterile branches, but here they are placed vertically and the bases connivent, so that the effect of the whole is that of a pinnatifid leaf. The fertile branches, however, have the leaves spirally arranged, and in the sterile ones the three-sided apical cell is found. The leaves, with few exceptions, e. g., Fontinalis, have a well- marked midrib, and the lamina is single-layered. Leucobryum (Fig. 121, A) has leaves made up of two or three layers of cells, large hyaline ones, somewhat as in Sphagnum, and small green cells. The hyaline cells, as in Sphagnum, have round holes in the walls, but no thickenings. The midrib may be narrow, as in Funaria, or it may occupy nearly the whole breadth of the leaf, as in the Polytrichacese, where, owing to the almost complete suppression of the lamina, secondary ver- tical plates of green cells are formed (Fig. 121, B). The one-third divergence of the leaves found in Fontinalis^ is replaced in most other genera by a larger divergence. (Goebel (8) ). Thus in Funaria hygrometrica it is f ; in Poly- trichum commune ^; in P. formosum if. As the archegonia are borne upon lateral branches, or upon the main axis, the stegocarpous Bryinese are frequently divided into two main divisions, the Pleurocarpse and the Acrocarpae, which are in turn divided into a number of subdivisions or families. How far the division into acrocarpous and pleuro- carpous forms is a natural one may be doubted, as probably the latter are secondary, and it is quite conceivable that different families of pleurocarpous forms may have originated inde- pendently from acrocarpous ones. The simplest of the stegocarpous Mosses, while having the operculum well marked, have no peristome. Thus the genus Gymnostomum has no peristome at all, and in an allied genus, Hymenostomwn, it is represented by a thin membrane covering the top of the columella. In nearly related genera, however, e. g., Weisia, a genuine peristome is present. The Tetraphidese, represented by the genus Tetraphis (Georgia) (Fig. 118), are interesting as showing the possible origin of the peristome, as well as some other interesting points ^ This seems to be strictly the case only in the smaller branches ; in the larges axes the leaves are not exactly in three rows. w. THE BRYALES ±1^ of structure. Tetraphis pellucida is a small Moss, which at the apex of its vegetative branches bears peculiar receptacles containing multicellular gemmae of a very characteristic form. The leaves that form the receptacle are smaller than the stem leaves, and closely set so as to form a sort of cup in which the gemmae are produced in large numbers. These arise as slender multicellular hairs, the end cell of which enlarges and forms a disc, at first one-layered, but later, by the walls parallel to the broad surfaces, becoming thicker in the middle, and lenticular Fig. ii8. — Tetraphis pellucida. A, Plant with gemmae, X6; B, upper part of the same, X50; C, young gemma, X600; D, a fully-developed gemma, X300. in form. The arrangement of the cells in the young gemmae looks as if the growth of the bud was due to a two-sided apical cell (Fig. 118, C), but this point was not positively determined. These gemmae give rise to a protonema of a peculiar form, from which in the usual way the leafy stems develop. The proto- nemal filaments grow into flat thalloid expansions that recall those of Sphagnum and Andrecua. 220 MOSSES AND FERNS CHAP, The sporogonium of Tetraphis has a peristome of pecuHar structure, and not strictly comparable to that of any of the other Mosses. After the operculum falls off the tissue lying beneath splits into four pointed teeth, which, however, are not, as in Funaria, composed simply of the cell walls, but are masses of tissue. All the other higher Bryales, with the exception of the Polytrichacese, have the peristome of essentially the same struc- ture as that described for Funaria. Sometimes the teeth do not separate but remain as a continuous membrane, e. g., the inner f'AA\f/fMf •• Sa • n o « Fig. 119. — A, Barhula fallax, upper part of the capsule, showing the slender twisted peristome teeth X about 20. B, Fontiualis antipyretica, showing double peristome (after Schimper). C, Polytrichum commune, peristome and epiphragma X8. D, P. commune, ripe capsule; i, with, 2, without the calyptra X3. peristome of Buxhaumia, or a perforated membrane, as in Fon- tinalis (Fig. 119, B). The base of the capsule, or apophysis, which Haberlandt (4) has shown to be the principal assimilative part of the sporo^: gonium, and which alone is provided with stomata, sometimes becomes very large, and in the genus Splachnum (Vaizy (i)) especially forms a largely-developed expanded body, which, must be looked upon as a specially-developed assimilating ap-: paratus. . - ;orL VI. THE BRYALES 221 Undoubtedly the Polytrichacese represent the highest stage of development among the Musci. This is true both in regard to the gametophore and the sporogonium. The former reaches in some species, e. g., P. commune, a length of 20 centimetres and sometimes more. The stem is usually angular and the closely-set leaves thick and rigid. The numerous rhizoids are often closely twisted together and form cable-like strands. The structure of the leaves is very characteristic, and differs very much from that of the simpler type found in Funaria. G Fig. 120. — Dawsonia superba. A, upper part of female plant bearing a sporogonium, Xi; B, a leaf, slightly enlarged; C, section of leaf, X about 70; D, part of the same more highly magnified; E, two views of the capsule, Xi^. In the Polytrichacese (Fig. 121) the midrib of the leaf is very broad and only at the extreme margin of the leaf is the lamina developed at all. A cross-section of the leaf shows that the midrib is greatly thickened in the centre, and gradually merges into the rudimentary lamina. In Dazvsonia (Fig. 120), the leaf is almost flat, in Polytrichiim (Fig. 121), usually more or less incurved at the margin. The outer, or dorsal, surface of the leaf is covered with a well marked epidermis, whose outer cell-walls are strongly 222 MOSSES AND FERNS chap. thickened, and have a conspicuous cuticle. Within this epi- dermis are closely set, small sclerenchymatous elongated cells, among which are found more or less definite rows of large, thin-walled elements, strongly suggesting the tracheary tissue of the vascular plants, and without much question, true water- conducting structures. From the inner ventral surface there arise numerous parallel, thin, vertical laminae (cl.) composed of green cells. These extend nearly the whole length of the leaves and in section appear as rows of short cells, the outer- most ones being somewhat enlarged. The axis of the shoot in the Polytrichaceae shows a decidedly complex structure and many reach a relatively large size. Thus in Dazvsonia snperba (Figs. 120, 122) it is about 1.5 mm. in diameter, and forms an erect, densely leafy shoot 40 to 50 centimetres in height. The cross-section of the shoot in the latter species (Fig. 122) is triangular in outline. Within the firm epidermis there are several layers of somewhat similar, but more compact cells, which like the epidermal cells are thick- walled, and dark coloured. This compact hypodermal tissue passes somewhat gradually into a colourless, parenchymatous ground-tissue, which makes up the bulk of the shoot-axis. There is a very conspicuous central cylinder composed of two tissue-elements — small, dark-colored sclerenchyma or fibrous tissue, especially compact toward the centre of the cylinder ; and very much larger, thin-walled cells, appearing almost destitute of protoplasmic contents, and closely resembling the vessels of true vascular plants, and like them, no doubt, true water-con- ducting organs. Traversing the ground tissue are slender strands of elongated cells — leaf-traces, which are structurally like the central cylinder of the shoot, but with the water- conducting cells less conspicuous. Most of the cells in the stem of Dawsonia, except the large tracheary cells of the central cylinder, contain starch, which it is stated by Goebel (8) is not abundant in the tissues of Polytrichum, where its place is taken largely by oil. Starch has been noted in Polytrichum in the outer cells of the stem and in the leaf-traces. The leaf-traces, or continuation of the central tissue of the midribs of the leaves, bend down into the stem, and finally unite with the axial cylinder of the latter, in a manner quite analogous to that found in the stems of many vascular plants. VI. THE BRYALES 223 Bastit ((i), p. 295), who has made a compar- ative study of the subter- ranean and aerial stems of P. jimiperiniim, divides the outer tissue of the lat- ter into epidermis, hypo- derma, and cortex. In the subterranean stems he finds the construction quite different from that of the leafv branches. The section of the former is triangular, and its epi- dermis provided with hairs which are absent from the epidermis of the aerial parts. Rudimen- tary scales, arranged in three rows, are present, and corresponding to these are strands of tissue that represent the leaf- traces of the aerial stems. The central cylinder is much larger relatively than in the leafy branches, and its cross-section is not continuous, but is inter- rupted by three "pericyclic sectors," composed of cells whose walls are but little thickened. The point of each sector is at the periphery of the me- dulla, or central cylinder, and the broad end toward the centre. As might be expected, intermediate con- ditions are found where the rhizome begins to grow upward to form a leafy branch. Fig. 121. — A, Transverse section of the leaf of Leucohryum; B, similar section of the leaf of Polytrichum commune; cl, chlorophyll-bear- ing cells (after Goebel). 224 MOSSES AND FERNS CHAP. The male inflorescence of the Polytrichaceae is especially conspicuous, as the leaves immediately surrounding the anther- idia are different both in form and colour from those of the stem. They are broad and membranaceous, and more or less distinctly reddish in colour. A well-known peculiarity of these forms is the fact that the growth of the stem is not stopped by the formation of antheridia, but after the latter have all been formed the axis resumes its growth and assumes the character of an ordinary leafy shoot. This, of course, indi- cates that, unlike most of the Mosses, the apical cell does not become transformed into an antheridium, and the researches of Fig. 122. — Dawsonia superba. A, Transverse section of the stem, X3S; B, part of the central cylinder, showing water-conducting elements, t, X200; C, outer tissues of the stem, X200. Hofmeister (2), Leitgeb (9), and Goebel (7) have shown that this is the case. The antheridia form groups at the base of each leaf of the inflorescence, and Leitgeb thinks it probable that each group represents a branch, i. e., the inflorescence is a compound structure, and not directly comparable to the simple male inflorescence of Funaria. The sporogonium in Poly- trichum has a large intercellular space between the inner spore- sac and columella as well as the one outside the outer spore-sac. In both cases the space is traversed by the conferva-like green filaments found in the other stegocarpous Mosses. The apoph- ysis is well developed, especially in Polytrichum, and the VI. THE BRYALES 225 calyptra very large and covered with a dense growth of hairs (Fig. 119, D). The structure of the peristome in the Polytrichaceae is entirely different from that of tlie other Mosses. It is com- posed of bundles of thickened fibrous cells arranged in crescent form, the ends of the crescent pointing up, and united with the adjacent end of the bundle next it. The tops of the teeth thus formed are connected by a layer of cells stretching across the opening like the head of a drum. This membrane is known technically as the ''Epiphragm" (Fig. 119, C). The Buxbaumiace^ The last group of Mosses to be considered is the very peculiar one of the Buxbaumiaceae. In these Mosses the Pig. 123. — A, Protonema of Buxbaumia indusiata, with the anthreidial shoot, X175; B, antheridium, seen in optical section ; C, sporophyte of B. sp., X4' (A, B, after Goebel.) gametophyte is extraordinarily reduced, although the sporo- gonium is large and well developed. So simple is the sexual plant, that Goebel (i6) has concluded that these ought to be taken away from the rest of the Mosses, and removed to a dis- tinct order. According to Goebel's account, the antheridia, which are long stalked, are borne directly upon the protonema, and subtended by a single colourless bract (Fig. 123). The female branches are also very rudimentary, but less so than the male. On the strength of the extreme simplicity of these. Goebel thinks that Biixhaumia is a primitive form allied to some alga-like progenitor of the Mosses. There are, however, two very strong objections to this. First the sporogonium, which 15 226 MOSSES AND FERNS chap. is extremely large, and complicated in structure, and essentially like that of the other stegocarpous Mosses; secondly, Bux- haumia has been shown by Haberlandt ((4), p. 480) to be distinctly suprophytic in its habits, and the extreme reduction of the assimilative tissue of the gametophyte is quite readily explicable from this cause. Fossil Muscine^ The remains of Muscinese in a fossil condition are exceed- ingly scanty ; so much so indeed as to practically throw no light upon the question of their origin and affinities, as nearly all of the forms discovered belong to the later formations, and are either identical with living species or closely allied forms. No doubt the great delicacy of the tissues of most of them, espe- cially the Hepaticse, accounts in great measure for their absence from the earlier geological formations. The Affinities of the Musci It is perfectly evident that the Mosses as a whole form a very clearly defined class, and that their relationship with other forms is at best a somewhat remote one. Sphagnum, however, certainly shows significant peculiarities that point to a connec- tion between this genus, at least, and the Hepaticse. It will be remembered that the protonema of Sphagnum is a large flat thallus, and not filamentous, as in most Bryales. It it note- worthy, however, that from the margin of this flat thallus later filamentous branches grow out which are apparently identical in structure with the ordinary protonemal filaments of the Bryales. In Andrecea similar flat thalloid protonemata occur, but not so largely developed as in Sphagnum, and finally in Tetraphis a similar condition of affairs is met with. As this occurs only among the lower members of the Moss series, the question naturally arises, does this have any phylogenetic mean- ing? While it is impossible to answer this question positively, it at any rate seems probable that it has a significance, and means that the protonema has been derived from a thalloid form related to some thallose Liverwort, and that by the sup- pression of the thalloid portion, as the leafy gametophore became more and more prominent, the filamentous branches, VI. THE BRYALES 227 which at first were mere appendages of the thalkis, finally came to be all that was left of it. The view of Goebel and others that the filamentous form of the protonema is the primitive one, and indicates an origin from alga-like ffjrms, might be maintained if the question were concerned simply with the prrjtonema ; but when the structure of the sexual organs, esjjecially the arche- gonium, is considered, and the development of the sporophyte, the difficulty of homologising these with the corresponding parts in any known Alga is apparent, while on the other hanrl the resemblance between them and those of the IlepaticcC is obvious. It is quite probable that the development of the fila- mentous protonema is a provision for the production of a greater number of gametophoric branches. As to which group of the Hepaticse comes the nearest to the Mosses, the answer is not doubtful. The remarkable simi- larity in the development and structure of the sporogonium of Sphagnum and the Anthocerotes leaves no room for doubt that as far as Sphagnum is concerned, the latter come nearest among existing forms to the ancestors of Sphagnujn. Of course this does not assume a direct connection between Sphagnum and any known form among the Anthocerotes. There are too many essential differences between the two to allow any such assumption : but that the two groups have come from a common stock is not impossible, and the structure of the capsule in Sphagnum points to some form which like Antho- ceros had a highly-developed assimilative system. This is indicated by the presence of stomata, which, aUhough function- less, probably were once perfect, and make it likely that with the great increase in the development of the gametophyte the sporophyte has lost to some extent its assimilative functions which have been assumed by the gametophyte. AndrecBa, both in regard to the gametophyte and the sporo- phyte, is in many ways intermediate between Sphagnum and the other Mosses. The resemblance in the dehiscence of the sporogonium to that of the Jungermanniaceae is probably acci- dental. It may perhaps be equally well compared to the split- ting of the upper part of the capsule into four parts, in Tctra- phis, although in the latter it is the inner tissue and not the epidermis which is thus divided. If this latter suggestion proves to be true, then there would be a direct connection of Andrecca with the stegocarpous 228 MOSSES AND FERNS ciiap. Bryales, and not through the cleistocarpous forms. These latter would then all have to be considered as degraded forms derived from a stegocarpous type, unless, with Leitgeb, we consider them as a distinct line of development leading up to the higher Bryales, entirely independent of the Sphagnaceae, and with Archidium and Ephemerum as the simplest forms. His comparison of these forms with Notothylas, however, can- not be maintained with our present knowledge of that genus, and more evidence is needed before his view can be accepted; but the possibility of some such explanation of the cleistocarp- ous Bryales must be borne in mind in trying to assign them their place in the system. The objections to considering Buxbaumia a primitive type have been already given, and it is not necessary to repeat them. CHAPTER VII THE PTERIDOPHYTA-FILICINE^-OPHIOGLOSSACE^ In tracing the evolution of the Bryophytes from the lowest to the highest types the gradual increase in the importance of the second generation, the sporophyte, is very manifest. This may or may not be accompanied by a corresponding development of the gametophyte. In the line of development represented by the higher Mosses, in a general way the two have been parallel, and the most highly differentiated gametophyte bears the most complicated sporophyte, as may be seen in Polytricluim, for example; but in the Hepatic^e this is not the case, and among the Anthocerotes much the most highly organised sporophyte, that of Anthoceros, is produced by a very simple gametophyte. In this evolution of the sporophyte, it approaches a condition where it is self-supporting, but in no case does it become abso- lutely so. A special assimilative tissue, it is true, is developed, and in some of the true Mosses, such as Splachnum, this goes so far that a special organ, the apophysis, is formed; but, as we have seen, the sporogonium is dependent for its supply of water and nitrogenous food upon the gametophyte, with which it remains intimately associated, and upon which it lives as a parasite. The type of structure found in the gametophyte of the Muscinese seems to be imperfectly fitted for a strictly terres- trial life. The gametophyte of all Archegoniates is more or less amphibious. Free water is essential for the act of fecundation, and the gametophyte seems never to have solved satisfactorily the problem of an adequate water supply, except by returning to the aquatic condition. 229 230 MOSSES AND FERNS chap. Many Bryophytes can exist only in damp, shady localities, and those which have adapted themselves to a xerophytic habit, have acquired the power of becoming completely dried up with- out being killed, reviving promptly when supplied with water, but remaining completely dormant during the period of drought. These plants do not depend upon their rhizoids for absorbing water, but, like Algae, can absorb water at all points of their surface. Where the plant depends largely upon the rhizoids for water absorption, as in the Marchantiacese, the plant is a flat, prostrate thallus, which offers a large surface for the development of the rhizoids. In the upright stems of the larger Mosses, the rhizoids are multicellular, and sometimes twisted into root-like strands, which are of relatively large size, and are undoubtedly efficient organs for water-absorption. Still it is evident that even such strands of multicellular rhizoids w^ould not suffice for providing the water necessary to make good the loss by transpiration in a large terrestrial plant. It is this failure to develop an adequate root system which prob- ably explains the fact that no Bryophyte has attained the dignity of a successful upright terrestrial plant. Among the Pteridophytes the gametophyte is equally in- capable of a strictly terrestrial existence; but in these plants, the sporophyte, developing still further along lines indicated in many Bryophytes, has finally attained to the condition of an independent plant. It may be conjectured that from part of the foot, the absorbent organ of the embryo in the bryophytic sporophyte, there was developed a root, with a permanent grow- ing point, and capable of indefinite growth in length. This, penetrating through the tissues of the gametophyte, put the sporophyte into direct communication with the water in the earth, and thus completely emancipated it from its former status of dependence upon the gametophyte. The true root differs essentially from the rhizoids in being a massive organ capable of indefinite growth and division, which can thus keep pace in its development with the increasing size and complexity of the sporophyte. The latter from this time assumes more and more the principal role in the life- history of the organism, while the gametophyte becomes corre- spondingly reduced. With the development of an independent sporophyte, there appeared a plant adapted from the first to a terrestrial existence and not a modification of an originally VII PTERIDOPHYTA—FILICJNEJE—OPIJJOCI.OSSACRAi 231 aquatic organism like the gametophyte of all Muscineae. In the few cases where true roots are absent their phce is taken by other structures that perform their functions. The assimilative activity is restricted to special organs, the leaves, except in a few cases where these become much reduced, as in Psilotum or Eqiii- sctmn. A main axis is present upon which the leaves are borne as appendages, and this continues to form new leaves and roots as long as the sporophyte li^/es. The differentiation of these special organs begins while the sporophyte is still very young. The earliest divisions in the embryo correspond closely to those in the embryo of a liryo- phyte, but instead of forming simply a capsule, as in all the Bryophytes, there is established more than one growing point, each one forming a distinct organ. In the typical Ferns there are four of these primary growing points, giving rise respect- ively to the stem, leaf, root and foot. The latter is a tem- porary structure, by which the young sporophyte absorbs food from the gametophyte, but as soon as it becomes independent the foot gradually withers away, and soon all trace of it is lost. The originally homogeneous tissues of the embryo become differentiated into the extremely complicated and varied tissues characterising the mature sporophyte. The most characteris- tic of these is the vascular system of tissues. This is hinted at in the central strand of tissue in the seta of many Mosses, and the columella of the Anthocerotes ; but in no Bryophyte does it reach the perfect development found in the Ferns and their relations, which are often called on this account the Vascular Cryptogams. The gradual reduction in the vegetative parts of the game- tophyte, from the large long-lived prothallium of the Marat- tiacere to the excessively reduced one found in the heterosporous Pteridophytes, has already been referred to in the introductory chapter. The structure of the sexual organs of the Pteridophytes appears at first sight radically different from that of the Bryophytes, but a careful comparison of the lower forms of the former with some of the Hepaticse, and especially with the Anthocerotes, shows that the difference is not so great as it at first sight appears. A further discussion of this point must be left, however, until we have considered more in detail the struc- ture of these parts in the different groups of the Pteridophytes, 212 MOSSES AND FERNS chap. where they are remarkably uniform. In all of them the arche- gonium has usually a neck composed of but four rows of per- ipheral cells, instead of five or six, as in the Bryophytes, and the antheridium, except in the leptosporangiate Ferns, is more or less completely sunk in the tissue of the prothallium. The spermatozoids are either biciliate, as in Mosses, or multiciliate, a condition which, so far as is known, does not exist among the Bryophytes. The formation of spores is very much more subordinated to the vegetative life of the sporophyte than is the case among the most highly organised of the Bryophytes. Indeed it may be many years before any signs of spore formation can be seen. The spores are always born in special organs, sporangia, which are for the most part outgrow^ths of the leaves, but may in a few cases develop from the stem. In the simplest cases the spores arise from a group of hypodermal cells, generally trace- able to a single primary cell. The cell outside of these divides to form a several-layered wall, but the limits of the sporangium are not definite, and it may scarcely project at all above the general surface of the leaf. From this "eusporangiate" condi- tion found in Ophioglossum, there is a complete series of forms leading to the so-called leptosporangiate type, where the whole sporangium is directly traceable to a single epidermal cell, and where a very regular series of divisions takes place before the archesporium is finally formed. With very few exceptions all of the existing Pteridophytes fall naturally into three series or classes of very unequal size. The first of these, the Ferns or Filicinese, is the predominant one at present, and includes at least nine-tenths of all living Pteridophytes. The Equisetinese are the most poorly repre- sented of the modern groups, and include but a single genus with about twenty-five species. The third class, the Lyco- podinese, is much richer both in genera and species than the Equisetinese, but much inferior in both to the Filicinese. The disproportion between these groups was much less marked in the earlier periods in the world's history, as is attested by the very numerous and perfect remains of Pteridophytes occurring especially in the coal-measures. At that time both the Equisetinese and Lycopodinese were much better developed both in regard to size and numbers than they are at present. VII PTERIDOPHYTA—FIUCINEAl—OPHIOGLOSSACEAi 2:sZ Class I. Filicine.^ (Filicales) The Filicinese or Filicales, as already stated, include by far the greater number of existing Pteridophytes, and are much more extended in range and abundant in numbers than either of the other classes. A marked characteristic of all Ferns is the large size of the leaves, which are also extremely complicated in form in many of them. In a few of these the leaves are simple, e. g., Ophioglossiim, Vittaria, I'ihilaria, but more com- monly they are pinnately compound and sometimes of enormous size. The stem varies a good deal in form and may be very short and completely subterranean, as in species of Ophioglos- siim and Botrychium, or it may be a creeping rhizome, or in some of the large tropical Ferns it is upright, and grows to a height of 8 to lo metres, or even more. While some forms of the Ferns are found adapted to almost all situations, most of them are moisture-loving plants, and reach their greatest development in the damp mountain forests of the tropics. A few, e. g., Ceratoptcris, AzoUa, are genuine aquatics, and still others, c. g., species of Gymnogrammc, live where they become absolutely dried up for several months each year. These latter will quickly revive, however, as soon as placed in water, and begin to grow at once. In the tropical and semi-tropical regions many Ferns are epiphytes, and form a most striking feature of the forest vegetation. With few ex- ceptions the sporophyte is long-lived, but a few species are annual, e. g., Ceratopteris, and depend mainly upon the spores for carrying the plant through from one season to another. The sporophyte may give rise to others by simply branching in the ordinary way, or special buds may be developed either from the stem or upon the leaves (Cystopteris hulhifera). Besides the normal production of the gametophyte from the spore, it may arise in various ways directly from the sporophyte (apospory) ; and conversely the latter may develop as a bud from the gametophyte without the intervention of the sexual organs (apogamy). The Filicinese include both eusporangiate and leptospo- rangiate forms, — indeed the latter occur only here. The former comprise the homosporous orders, Ophioglossales and Maratti- ales, and possibly the heterosporous order Isoetales, whose sys- tematic position, however, it mustrns. The whole epibasal part of the embryo is devoted to the for- mation of the foot, in this respect showing an analogy, at least with Anthoccros. From the epibasal region arise the shoot and the root, both of which later develop a definite ai)ical cell. The initial cell of the root at once begins to form ])ericlinal cells, which cut ofif the segments of the root caj) from its fjuter face, and the apical cell thus becomes deeply sunk beneath the surface of the root-apex, which projects but little beyond the other parts of the very massive embryo-sporophyte. The primary leaf, or cotyledon (Fig. 130 cot.), unlike that of the true Ferns, arises secondarily from the shoot. In one instance, Jeffrey found small tracheids present in a prothallium, but the young sporophyte had been destroyed, and there w^as no means of determining whether this formation of tracheids was associated with apogamy, as in all other similar cases that have been observed. The tissues adjacent to the venter of the archegonium grow rapidly, keeping pace with the developing embryo, which becomes very large before it breaks through the overlying tissues (calyptra), which protect it. At this time, the very large foot is especially conspicuous. The root is already some- what elongated and show^s a very definite arrangement of its tissues, which resembles that of the later roots. A tetrahedral apical cell is covered by a root-cap composed of several layers of cells, and the axis of the root is occupied by a strand of nar- row cells, which later develop into the vascular cylinder or ''stele" of the root. The cotyledon, at this time, is relatively inconspicuous, and forms a short, incurved, conical protuberance, between which and the root lies the very slightly conical apex of the shoot. Both stem and leaf show a fairly distinct apical cell, but these apparently cannot be traced back to the original embryo-octants, as is the case in the more specialised Ferns. A very short procambium cylinder can somewhat later be seen in the axis of the stem, and from it extends a similar strand into the cotyle- don. The central cylinder of the stem (Jeffrey (i), p. 21) becomes fully developed below the point of origin of the cotyledon. From the first it is a hollow cylinder with a well- 244 MOSSES AND FERNS chap. marked pith. The vascular ring is broken by a gap above the first leaf-trace ( cotyledonary stele), and the pith is thus thrown into communication with the outer ground tissue, or cortex. The first tracheary tissue appears shortly after the root has broken through the calyptra, at which time the root has the length of 5-20 millimetres. The development of the tracheary tissue in the root begins at two, or more commonly three, points, i. e., the root is either "diarch" or "triarch." The in- nermost layer of the fundamental tissue forms the "endoder- mis" or bundle-sheath. As is usually the case, the endodermal cells are characterised by the peculiar thickening or foldings of the radial walls, which appear as elongated dots in transverse sections. A similar endodermis can be made out, surrounding the stelar tube of the stem. The primary tracheids, or "protoxylem," have reticulately sculptured walls, and, except in size, closely resemble the secon- dary tracheary elements, or "metaxylem," which are formed centripetally, and meet in the centre of the vascular cylinder. Between the xylem masses are as many masses of phloem, or bast, made up in part of sieve-tubes with which are mingled elongated paranchyma cells. Surrounding the circle of xylem and phloem masses is the pericycle, composed of one or two layers of parenchyma. After the young root has broken through the calyptra and penetrated the ground, the cotyledon grows upward and finally makes its appearance above the surface of the ground. It becomes differentiated into a slender, nearly cylindrical stalk (stipe) and a much-divided lamina (Fig. 127, E). The single primary vascular bundle of the leaf-rudiment divides into two within the stalk, and passes into the two lateral lobes of the lamina. From one of them a strong branch is developed which constitutes the midrib of the central segment of the lamina. The vascular bundles of the stipe approach the collateral type, rather than the concentric structure found in the later formed leaves. Sometimes two or three roots are developed before the cotyledon unfolds, and the young sporophyte remains for a long time — probably two or three years — attached to the gameto- phyte, the superficial cells of the foot remaining active during this period. These cells show the dense cytoplasm and con- spicuous nuclei of active cells. . -- VII PTERIDOPHYTA—FILICINE^—OPHIOGLOSSACEJE 245 According to Mettenius, the cotyledon in OpJiioglossum pednncnlosmn develops much earlier than is the case in Botrychhim. It appears above the ground while the primary root is still but little developed. (Fig. 125, B.) In Botrychium lunaria, according to Hofmeister, the first three leaves are rudimentary and the first green leaf does not appear above ground until the second year. Mettenius' account of the development of the embryo in O. pedunculosum is less complete. The earliest stage seen by him was already multicellular, and the young embryo had the form of an oval cell mass in which the primary divisions were not recognisable. The upper part, i. e., that next the arche- gonium. neck, grows up at ^once into the cotyledon, while the opposite part gives rise to the first root. These grow respect- ively upw^ard and downward*, and break through the overlying prothallial cells. Later, at a point between the two, the stem apex is developed. The first leaf becomes green, and develops a lamina similar to that of the later-formed ones. Usually but one embryo is developed from the prothallium, but occasionally two are formed, especially where the prothallium forks. The Adult Sporophyfe Ophioglossiim (Ophioderma) pendulum, an epiphyte com- mon in the Eastern tropics, may be taken as a type of the sim- plest of the Ophioglossacese. Its short creeping stem grows upon the trunks of trees, especially tree-ferns, from which the long flaccid leaves hang down. The lamina of the leaf merges insensibly into the stout petiole whose fleshy base forms a sheath about the next younger leaf. Corresponding to each leaf is a thick unbranched root, which penetrates into the crevices of the bark and holds the plant secure. These roots are smooth, and show no trace of rhizoids. The petiole is continued up into the lamina as a very broad and thick midrib, which in the spo- riferous leaves (sporophylls) is continued into the peculiar elongated spike which bears the sporangia. The petiole if cut across shows a number of vascular bundles arranged in a single row, nearly concentric with the periphery of the section. As these enter the lamina they anastomose and form a network with elongated meshes (Fig. 133, C) and no free ends. Sections of the spike cut parallel to its broad Fig. 13:. — Ophioglossiim pendulum. A, Leaf with sporangiophore, natrual size; B, cross-section of the petiole, X6; C, section of the sporangiophore, parallel to tts broad surface, X6. VII PTERIDOPHYTA—FILICINEJE—OPHIOGLOSSACE^ 24.7 diameter show a somewhat similar arran<^rement of the vascular bundles, but here there are free brandies exteiKhng between the sporangia. The relations of the bundles of the fertile and sterile parts of the leaf are best followed in the smaller species. Prantl ((7), p. 155) describes it as fol- lows for O. Liisitanicum, and states that it is essen- tially the same in other species. ''The primary bundle given off from the stem branches just after it enters the petiole. The main bundle gives off two smaller lateral branches right and left. The latter branch again near the base of the sporangiophore,and the upper branches from each unite to form the sin- gle bundle that enters the latter." The sporangia are sunk in the tissue of the sporophyll, and scarcely project at all above the surface, where the position of each one is indicated by a faint transverse fur- row which marks the place where it opens. Seen in sections parallel to the flat surface these ap- pear perfectly round, but .^ in transverse section are^ kidney-shaped (Fig. 140, C). The apex of the stem forms a blunt cone, which, however, is not visible from the outside. A longitudinal section through the end of the stem shows that it is covered by a sheath com- FiG. 1^2.^0 phioglossum vulgaUim, X i. 24« MOSSES AND FERNS CHAP. posed of several layers of cells, and this encloses a cavity in which are the growing point of the stem and the youngest leaf. The leaves here form much more rapidly than in the species of the temperate regions, as the growth continues uninterruptedly throughout the year. The real apex of the stem forms an in- clined nearly plane surface, slightly raised in the centre, where the single apical cell is placed (Fig. i34,A,B). This cell is by no means conspicuous, and not always readily found, but probably is always present. It has the form of an inverted three-sided pyramid, but the lateral faces are more or less strongly convex, and the apex may be truncate. From the few cases observed it is not possible to say whether in addition to the three sets of lateral segments basal seg- ments are also formed, but it is by no means impossible that such is the case. Ac- cording to investigations of Rostowzew ((i), p. 451), the apical cell of the stem of Ophioglossiim vulgatum shows considerable variation, and may be either a three or four-sided prism, i. e., it ap- ^ , . , , , . ,, parently also may have the riG. 133. — Ophioglossuni pendulum. A, Me- | -^ > / \ dian longitudinal section of stem apex, X4; uaSC trUnCatC. JriOlle S \^ ) ^, the growing point; B, young sporophyll, ^gg^j.-^jQj^ ag-rCCS with this X2; sp, the sporangiophore; C, an older '- ^ leaf, showing the venation, X2. CXCCpt that he StatCS that he always found the cell pointed below, not truncate. The segments cut off from the lateral faces are large, and the divisions irregular. They are appar- ently formed in very slow succession, and the irregularity of the succeeding divisions in the segments themselves soon makes it impossible to trace their limits. Each segment apparently gives rise to a leaf, but this is impossible to determine with certainty. The first wall in the young segment probably divides it into an inner and outer cell, but the next divisions could not be deter- VII PTERIDOPHYTA—FILICINEJE—OPHIOGLOSSACEJE 249 mined positively. Probably, as in Botrychium, the outer cell is next divided by a vertical wall, ])erpendicular to the broad faces of the segment, into two cells, in which divisions then take place in both transverse and longitudinal direction without strict regularity. The stem in O. pendulum is mostly made up of thin-wallcd parenchyma, and the vascular bundles are much less developed than is the case in the underground stem of O. vulgatiim or Botrychium. The bundles are of the collateral form, /. c, the inner side is occupied by the xylem, the outer by the phloem, Fig. 134.^-Ophioglossum pendulum. A, Longitudinal section of stem apex, X6o; B, the central part of the same section, Xi8o; D, longitudinal section of very young sporangiophore, Xi8o; E, cross-section of young sporangiophore, X6o. and there is no evident bundle-sheath developed. The bundles form a very irregular wide-meshed cylinder, not differing essen- tially from that in O. vulgattui Van Tieghem (7) states that in Ophioglossum vuJgatum each vascular strand is completely invested with a distinct endodermis and pericycle; but Bower (16) found the endoder- mis very poorly developed in the species studied by him, especially 0. Bergianum, a small and simple species. The stem of this form shows in transverse section two strands which may 250 MOSSES AND FERNS chap. either be separate, or partly coherent, so as to form a single crescent-shaped bundle, when seen in section. There may be, however, even in this species, more than two strands present. Poirault (2) found a definite endodermis in the lower part of the stem, which disappears in the upper portion. Van Tieghem asserts (see Bower (16), p. 67) that in the young sporophyte of O. vulgatum, there is at first a solid axial stele, with pericycle and endodermis, and that only above the insertion of the first leaf does a pith appear. In the bundles of the stem of 0. pendulum, the xylem of the collateral bundle is mainly composed of short irregular tracheids, with close reticulate markings on the walls. The phloem is composed of short, thin-walled cells with large nuclei. No true sieve-tubes could be recognised. The Leaf The young leaf is completely concealed by the sheath formed at the base of the next older one. It is at first a conical pro- tuberance arising close to the stem apex, around which its base gradually grows and forms the sheath about it and the next leaf rudiment. It is probable that here, as in 0. vulgatum,^ the young leaf grows at first by a definite apical cell. After the plant has reached a certain age, each leaf gives rise to 3. sporangial spike, which becomes evident while the leaf is still very small. The first indication of this is a conical outgrowth upon the inner surface of the leaf, about halfway between the apex and base. A longitudinal section of this shows it to be made up of large cells, especially toward the top ; but although there was sometimes an appearance that indicated the presence of a single apical cell, this was by no means certain, and if there is such an initial cell, its divisions must be very irregular. Bower (16) found that in O. vulgatum the young spo- rangial spike grows from a single apical cell, which in less robust specimens persists for a long time as a four-sided, initial cell, but in the larger specimens seems to be replaced by four similar initials. The subsequent growth of the leaf is for a long time mainly from the base, and the young sporangial spike is much nearer the apex in the next stage (Fig. 133, B). No distinct petiole ^ Rostowzew (i); p. 451. VII PTERIDOPHYTA—FILICINEJE—OPHIOGLOSSACEJE 251 has yet developed, but the centre of the young leaf, up to the point of attachment of the spike, is traversed by the thick mid- rib, above which the lamina is still very small. Indeed in this stage it looks as if the spike were really terminal and the lamina a lateral appendage. The young spike now forms a beak- shaped body curving inward and upward, and sections of slightly older stages than the one figured show the first indica- tions of the developing sporangia. Later still the base of the leaf becomes narrowed into the petiole, and the spike also becomes divided into the upper sporiferous portion and the short slender pedicel. The anatomical structure of the leaf is extremely simple. The epidermis is composed of rather thick-walled cells, irreg- ularly polygonal in outline, with large stomata at intervals, about which the cells are ar- ranged concentrically, and fre- quently with a good deal of regularity. The stomata them- selves (Fig. 135), seen from above, have an angular outline, but from below are perfectly oval, and cross-sections show that this appearance is due to a partial overarching of the guard cells of the stoma by the surrounding epidermal cells. The upper walls of the guard cells are thickened unequally, giving them the appearance of being folded longitudinally. There is no distinct hypoderma formed, and the bulk of the leaf is made up of a uniform mesophyll composed of nearly globular cells with much chlorophyll, and separated by numerous inter- cellular spaces. In the petiole the tissues are similar, but more compact, and the walls of the ground tissue are all deeply pitted. The vascular bundles are nearly circular in section and show a compact mass of tracheary tissue (Fig. 136, t), surrounded by nearly uniform cells with moderately thick colourless walls. The limits of the bundle are not, as in the higher Ferns, marked by a distinct bundle-sheath, but are indicated simply by the Fig. 135. — Stoma from the leaf of Ophio- glossum pendulum, X260. ^5^ MOSSES AND FERNS CHAP. somewhat smaller size of the cells of the bundle itself — indeed it is not always easy to say exactly where the ground tissue begins. The xylem is composed of pointed tracheids whose walls are marked with thick reticulate bands. This mass of tracheary tissue is situated near the inner side of the bundle, which like that of the stem is collateral. The rest of the bundle is composed of sieve-tubes mingled irregularly with smaller cambiform cells. Whether or not sieve-tubes occur upon the inner side of the bundle could not be positively deter- mined. The sieve-tubes have transverse walls, and in 0. vul- FiG. 136. — Vascular bundle of the petiole of O. pendulum, X260; t, t, the xylem of the bundle. gatiim lateral sieve-plates have been observed. The spo- rangiophore has much the same anatomical structure as the rest of the leaf, but stomata are quite absent from its epidermis. In this respect O. pendulum differs from O. vulgatum and allied species, where stomata are developed upon the spo- rangiophore as well as upon the rest of the leaf. The Root The roots are formed singly near the bases of the leaves, and are light yellowish brown in colour, and so far as could be VII PTERIDOPHYTA—FILICINEJE—OPHIOGLOSSACEJE 253 seen, entirely unbranched. Sections show that here, as in most vascular plants, the growing point of the root is not at the apex, but some distance below and protected by the root-cap. The growth of the root in Ophioglossuin can be traced to a single apical cell (Fig. 137), which is of large size, and, like that of the stem, approximately pyramidal in form. While the divi- sions show greater regularity than in the stem, still they are very much less so than in the leptosporangiate Ferns. Seg- ments are cut off not only from the lateral faces of the apical cell, but also from its outer face. These outer segments help to form the root-cap, which, however, is not derived exclusively Fig. i27.^0phioglossum pendulum. A, Longitudinal; B, transverse sections of the root apex, X215. from these, but In part also from the outer cells of the lateral segments. Each of the latter is first divided by a nearly ver- tical wall, perpendicular to its broad faces, into two "sextant cells," but beyond this no regularity could be discovered in the order of division in the segments, and the tissue at the growing- point, especially in longitudinal section, presents a very con- fused arrangement of the cells. A little lower down two regions are discernible, a central cylinder (plerome), whose limits are not very clearly defined, and the periblem or cortex. A definite epidermis is not distinguishable. The first permanent tissue in the plerome cylinder or stele, which is elliptical in section, arises in the form of small tracheids 254 MOSSES AND FERNS CHAP. near the foci of the elhptical section. From here the formation proceeds towards the centre, and in the full-grown root the tracheary tissue forms a continuous band occupying the larger axis of the section, the last-formed tracheids being the largest. On either side of this tracheary plate is a poorly defined mass of phloem, similar to that of the stem and leaf bundles. An en- dodermis or bundle sheath can be made out, although it is much less prominent than in most roots. The endodermis is derived from the innermost cortical layer, and the radial cell-walls are characterised by a thickening, or folding of the wall. In O. vul- gatum the bundle of the root is diarch to begin with, but by the suppression of one of the phloem masses it becomes monarch. The Sporangium The development of the sporangium has been studied by Goebel ((17), p. 390), in O. vulgatum, and recently by Bower (16) in this species and in 0. pendulum. The latter has been carefully examined by the writer, and the re- FiG. z3S.-0.pendulum.^ Vascular bundle of the root, g^j^g confirm that of Xos. The phloem is shaded; en^ endodermis. the latter investigator, except that it seems possible that the archesporium may be traced to a single cell, as Goebel asserts is probably the case in O.vul gatum. According to Bower (16), in all species examined by him, the sporangia arise from a continuous band of superficial tissue, on each side of the spike. To this he gives the name, "sporan- giogenic band." The sporangia arise from the sporangiogenic band, at more or less definite intervals, separated by intervals of sterile cells. In the sporangial areas, periclinal walls sep- VII PTERIDOPHYTA—FILICINE^—OPHIOGLOSSACEJE 255 arate an inner archesporium from the outer cells, destined to form the wall of the sporangium. Between the young spo- rangia the cells form sterile septa. The cell-groups which form archesporia, and those which develop into sterile septa, are sister-cell groups. All of the sporogenous tissue cannot be traced back to the primary archesporial cell, as later secondary sporogenous tissue may be formed by further periclinal divisions in the outer cells of the sporangium. A transverse section of the very young sporangiophore is A. B. Fig. 139. — A, Very young; B, older sporangia of O. pendulum; transverse sections, X260. somewhat triangular, the broader side corresponding to the outer surface of the sporangiophore. The cells are very irreg- ular in form, and no differentiation of the tissues is to be observed. Sections of somewhat older stages show in some cases, at least, a large epidermal cell occupying nearly the centre of the shorter sides of the triangular section. This cell has a larger nucleus than its neighbours, and is decidedly broader. The next stage was not observed, but a somewhat more advanced one shows a small group of inner cells (shaded in the figure), which appear to have arisen from the primary 256 MOSSES AND FERNS CHAP. cell by a transverse wall, although this point is exceedingly difficult to determine on account of the great similarity of all the cells (Fig. 139). This group of inner cells (or the single one from which they perhaps come) constitutes the arche- sporium, and by rapid division in all directions forms a large mass of cells whose contents become denser than those of the Fig. 140. — Ophioglossum pendulum. A, Section of a young sporangium, the arch- esporial tissue is shaded, the inner cells with dark nuclei being the definitive sporogenous cells, X200; B, transverse section of an older sporangium; sp, sporangeous cells; t, tapetum, X about 35; C, a portion of B more highly magni- fied; D, section of nearly mature sporangial spike, X8. surrounding ones, between which and these, however, the limits are not very plain. Later, when the number of cells is com- plete, the difference between them and the sterile tissue of the sporangiophore is much more evident. The cells lying outside of the archesporium divide rapidly both by longitudinal and transverse walls, and form the thick outer wall of the sporangium. In longitudinal sections, two VII PTERIDOPHYTA—FILICINE^—OPHIOGLOSSACE^ 2S7 rows of cells may be seen extending from the mass of arche- sporial cells to the periphery. In these rows the vertical walls have been more numerous than in the adjacent ones, so that the number of cells in these rows is greater. It is between these rows of cells that the cleft is formed by which the ripe sporangium opens. The outer cells of the sporogenous tissue do not develop into spores, but constitute the "tapetum" (Fig. 140, B, t), which serves to nourish ihe developing spores. After the full number of cells is reached in the archesporium, their walls become partially disorganized, and the cells round off and separate, exactly as in the sporogonium of a Bryophyte, and each cell is, potentially at least, a spore mother cell. Bower (16) states that only a part of the cells produce spores, and that the rest remain sterile and serve with the disorganised tapetal cells to nourish the growing spores. The final division of the spore mother cells into four spores is identical with that of the Bryophytes. At maturity the sporangium opens by a cleft, whose position is indicated as we have seen in the younger stages, and as the cells shrink with the drying of the ripe sporangiophore the spores are forced out through this cleft. Ophioglossum vulgatum and the other terrestrial forms show some points of difference when compared with 0. pen- dulum. These grow much more slowly, and longitudinal sec- tions of the upper part of the subterranean stem show several leaves in different stages of development. Each leaf rudiment, as in O. pendulum, is covered by a conical sheath, formed at the base of the next older leaf, and these sheaths are open at the top, so that there is direct communication between the outside air and the youngest of these sheaths which encloses, as in the latter species, the youngest leaf rudiment and stem apex (Ros- towzew ( I ) , p. 45 1 ) . In these terrestrial forms, also, the sporangiophore is longer stalked, and the lamina of the leaf more clearly separated from the petiole, which is not continued into it. The lamina is relatively broader and the venation more complex, in some species showing also free endings to the ulti- mate branches. The sporangia, too, project more strongly and are very evident (Fig. 132). Branching of the roots occurs occasionally, and according to Rostowzew may be either spurious or genuine. In the first place an adventive bud, which ordinarily would develop into a stem, develops a single root and 1.7 258 MOSSES AND FERNS chap. then ceases to grow. This root appears to be formed directly from the main root, and as the latter continues to grow the effect is that of a true dichotomy. The latter does occur, but not frequently. The formation of adventitious buds upon the roots is the principal method of propagation of some species of Ophioglos- siim, whose prothallia, as we have seen, are apparently very seldom developed. Rostowzew states that these are not de- veloped from the apical cell of the root, but arise from one of the younger segments, and the apical cell of the bud is produced from one of the outer cells of the young segment, but is covered by the root-cap, through which the bud afterwards breaks. The sheath covering the first leaf of the bud is formed from the cortex of the root and the root-cap. Differing most widely from the other species in general appearance is the curious epiphytic 0. (Cheiroglossa) palma- tiim. In this species the leaf is dichotomously branched, and instead of a single sporangiophore there are a number arranged in two rows along the sides of the upper part of the petiole and the base of the lamina. According to Bitter ( ( i ) p. 468) , 0. pendulum also has the sterile leaf segment dichotomously divided, but this was never the case in the specimens collected by the writer in various parts of the Hawaiian Islands. These invariably had an undivided, strap-shaped leaf. In O. Bergianuni the plant is very small and the sporangia are reduced in number to a dozen or less. The sterile segment is inserted very far down. A most remarkable form has been recently described from Sumatra (Bower (20) ). This species, O. simplex, is described as having no sterile leaf-segment, or the merest rudiment of one, the sporophyll being a flattened slender body, with the sporangia closely resembling those of O. pen- dulum, to which 0. simplex seems to be allied. O. simplex may be considered to represent the most primitive type of the genus yet discovered. BOTRYCHIUM The genus Botrychium includes several exceedingly variable species, the simplest forms, like B. simplex (Fig. 141, A, B), being very close to Ophioglossum, while leading from these is a VII PTERIDOPHYTA—FILICINEJE—OPIIIOGLOSSACEJE 250 series ending in much more complicated types, of which B. Vir- giniannm is a good example. In B. simplex the lamina of the leaf is either entirely undivided, as in most species of Ophioglus- siiiji, or once pinnatitid. From these there is a complete series to the ample decompound leaf (jf B. Virgiiiianiim. When the other parts of the plant are studied we find that this greater com- plexity extends to them as well. Thus the sporangiophore is also decompound, and the sporangia entirely free, showing an approach to those of such Ferns as Osmuucla; and the venation, wdiich in the simpler forms is dichotomous, approaches the pinnate type in B. P^irgiiiianiiiii. The tissues, especially the vascular bundles, are also more highly differentiated in the larger species. Under favourable conditions well-grown plants of B. I'ir- ginianuni reach a height of 50 cm. or more, and the sterile lamina of the leaf, which is triangular in outline, may be 30 to 40 cm. in breadth, and from three to four times pinnate. The texture of the leaf is membranaceous and not fleshv like that of Ophioglossujji and most species of Botrychium. The sporan- giophore is twice or thrice pinnate. The plant sends up a single leaf each year from the underground stem, which is upright and several centimetres in length in old specimens. The roots are thick and fleshy, and much smaller at the point of insertion. As in Ophioglossuin each root corresponds probably to a leaf, but the roots branch frequently, so that the root system is much better developed than in Ophioglossuin. The secondary roots of B. Viro-inianuiu arise laterallv, and in much the same way as those of the higher Ferns. As in the terrestrial species of Ophioglossnm, the development of the leaves is very slow. In most species of Botrychium the relation of the leaf base to the young bud and stem apex is the same as in Ophioglossnm, except that the sheath is more obviously formed from the leaf base ; but in B. V ir ginianum the sheath is open on one side, and more resembles a pair of stipules. Fig. 142, A shows the stem and terminal bud of a plant of this species with all but the base of the leaf of the present year cut away, and B the same with the bud cut open longitudinally. At this stage the parts of the leaf for the next year are well advanced, and the formation of the individual sporangia just begim. The leaf for the second year already shows the sporangiophore clearly evident, and the leaf which is to unfold in three years is evident, but the sporan- Fig. 141. — A, B, Botrychium simplex, slightly enlarged; C, B. ternatum, X % 5 D, leaf segment of B. lunaria; E, leaf segment of B. Virginianum, natural size; F, portion of sterile leaf segment of Helminthostachys Zeylanica; G, fragment of the sporan- giophore of the same enlarged. A, B, C after Luerssen; D, F after Hooker. VII P TERIDOPH Y TA—FILICINE/E—0 PIIIOGLOSSA CEAB 261 giophore not yet differentiated. At the base of the youngest leaf is the stem apex. The wliole bnd is covered in this species with numerous short hairs, which are also found in B. tcrnatum and some other species ; but in B. simplex and the other simpler species it is perfectly smooth, as in Ophiof^lossuiii. The young leaves in B. Virginianuni are bent over, and the segments of the leaf are bent inward in a way that recalls the vernation of the true Ferns. The sporangiophore grows out frrjin the inner surface of the lamina, and its branches are directed in the opposite direction from those of the sterile part of the leaf. B. Fig. 142. — Botrychium Virginianum. A, Rhizome and terminal bud of a strong plant, the roots and all but the base of the oldest leaf removed, X i ; B, longitudinal sec- tion of the bud, X3; st, the stem apex; I. II. III., the leaves; C, transverse sec- tion of the petiole, X4; D, transverse section of the rhizome, X about 16; P, the pith; m, medullary rays; x, xylem; c, cambium; ph, phloem; sh, endodermis. The vascular bundles of the stem are much more prominent than in Ophioglossum, and form a hollow cylinder, with small gaps only, corresponding to the leaves. This cylinder shows the tissues arranged in a manner that more nearly resembles the structure of the stem in Gymnosperms or normal Dicotyledons than anything else. Surrounding the central pith (Fig. 142, P) is a ring of woody tissue (.r) with radiating medullary rays (m), and outside of this a ring of phloem, separated from the 262 MOSSES AND FERNS chap. xylem by a zone of cambium (c), so that here alone among the Ferns the bundles are capable of secondary thickening. The whole cylinder is enclosed by a bundle-sheath (endodermis) consisting of a single layer of cells. The cortical part of the stem is mainly composed of starch- bearing parenchyma, but the outermost layers show a formation of cork, which also is developed in the cortical portions of the roots. The free surface of the stem apex is very narrow, and the cells about it correspondingly compressed. The apical cell (Fig. 143, A, B), seen in longitudinal section, is very deep and narrow, but as comparison of cross and longitudinal sections shows, has the characteristic pyramidal form, and here there is no doubt that only lateral segments are cut off from it. Holle's ( (i) PI. iv., Fig. 32) figure of Botrychium rutcefolmm closely resembles B. Virginianum, and probably the other species will show the same form of apical cell. The divisions are decidedly more regular in the segments of B. Virginianiim than in Ophio- glossum, and can be more easily followed, although here, too, as the division evidently proceeds very slowly, it is difficult to trace the limits of the segments beyond the first complete set, which in transverse section are sufficiently clear. The first division divides the segment into an inner and an outer cell, the former probably being directly the initial for the central cylinder. The outer cell by later divisions forms the cortex, and the epidermis which covers the very small exposed surface of the stem apex. As in Ophioglossum, it is impossible to determine exactly the method of origin of the young leaves, one of which probably corresponds to each segment of the apical cell, but as soon as the leaf can be recognised as such it is already a multicellular organ. It grows at first by an apical cell which seems to correspond closely in its growth with that of the stem. From almost the very first (Fig. 143) the growth of the leaf is stronger on the outer side, and in consequence it bends inward over the stem apex. The arrangement of the tissues of the fully-developed stem shows, as we have seen, a striking similarity to that in the stems of many Spermatophytes. The xylem of the strictly collateral bundle is made up principally of large prismatic tracheids (Fig. 144), whose walls are marked with bordered pits not unlike those so characteristic of the Coniferse, but some- VII PTERIDOPHYTA—FILICINEAl—OPHIOGLOSSACE^ 263 what intermediate between these and the elongated ones found in most Ferns. The vvahs between the pits are very much thickened, and the bottoms of corresponchng pits in the walls of adjacent tracheids are separated by a very delicate membrane. At intervals medullary rays, one cell thick, extend from the i)ith to the outer limit of the xylem. The cells are elongated radially, and have uniformly thickened walls and granular contents. The phloem consists of large sieve-tubes and similar but smaller parenchymatous cells. No bast fibres or sclerenchy- matous cells are present. The whole cylinder is bounded by Fig. 143. — Botrychium Virginianum. A, Longitudinal section of the stem apex o young plant, X260; B, cross-section of a similar specimen; L, the youngest leaf. of a a single layer of cells somewhat compressed radially, forming the endodermis or bundle-sheath. Between the xylem and phloem is a well-defined layer of cambium by whose growth the thickness of the vascular cylinder is slowly but constantly added to, and as a result there is a secondary growth of the stem strictly comparable to that of the Dicotyledons. The outer layer of the cortex (the epidermis is quite absent) develops cork, but not from a definite cork cambium (Holle, (i), p. 249). These cork cells arise by repeated tangential divisions in cells near the periphery, and have in consequence the same regular arrangement seen in similar cells of the higher plants. 264 MOSSES AND FERNS CHAP. A cross-section of the petiole of the earliest leaves of the young plant shows but a single nearly central vascular bundle, but as the plant grows older the number becomes much larger, and may reach ten (Luerssen (8), p. 58). In leaves of mod- erate size there are usually about four, and these are arranged symmetrically. The ground tissue is composed mainly of large thin-walled parenchyma and a well-marked epidermis. The fibrovascular bundles are arranged in two groups, right and left, and where there are four of them the inner ones are the O^ Fig. 144. — A, Part of a cross-section of the stem bundle of B. Virginianum, X200, — lettering as in Fig. 142; B, a portion of the tracheary tissue, showing the peculiarly pitted walls, X400. larger, and in cross-section crescent-shaped. The xylem occu- pies the middle of the section, and is completely surrounded by the phloem, i.e., the bundle is concentric, like that of the true Ferns. In B. lunaria the bundle has the phloem only perfectly developed on its outer side and approaches the collateral form. B. ternatum and B. lunaria, while having concentric bundles, also have the phloem more strongly developed on the outer side. The tracheary tissue is much like that of the stem, but the tracheids are smaller and the walls thinner. The smaller tra- cheids show reticulate markings. VII PTERIDOPHYTA—FIUCINEAI—OPHIOGLOSSACEJE 265 The phloem is composed also of the same elements, large sieve-tubes, arranged in a pretty definite zone next the xylem, and smaller cells of similar appearance, but not showing the multinucleate character or perforated transverse walls of the latter. The sieve-tubes are large (Fig. 145), and in longi- tudinal section are seen to consist of rows of wide cells with either horizontal or oblique division walls. The transverse walls separating two members of a sieve-tube are somewhat swollen and show small perforations, which are not always Fig. 145. — Part ot a vascular bundle from the petiole of B. Virginianum, X245; xy, xylem; ph, phloem; s, s, sieve-tubes; B, two sieve-tubes in longitudinal section, X490; sp, sieve-plates; n, nuclei. easily demonstrated. According to Janczewski (4) these pits do not penetrate the membrane between the cells, but Russow's (5) assumption that there is direct communication between the cells is correct, although difficult to prove. Russow also states that callus is present in the sieve-plates of Botrychmm, although poorly developed. According to Janczewski the pores are not confined to the transverse walls, but may also occur, but much less frequently, in the longitudinal walls. The contents of the 266 MOSSES AND FERNS CHAP. sieve-tubes consist of a thin parietal layer of protoplasm in which numerous nuclei are imbedded. Little glistening glob- ules are also found, especially close to the openings of the pores of the sieve-plates. The lamina of the sterile segment of the leaf is composed of a spongy green mesophyll, more compact on the upper sur- face. The epidermal cells show the wavy outlines characteristic of the broad leaves of other Ferns, and develop stomata only upon the lower side of the leaf. Fig. 146. — Botrychium Virginianum. A, Longitudinal; B, transverse sections of the root apex, X200; pi, plerome. The Root The roots arise singly at the bases of the leaves, and in older plants branch monopodially. Like those of Ophioglossum they have no root-hairs, but the smooth surface of the younger roots becomes often strongly wrinkled in the older ones. Sec- tions either transverse or longitudinal, through the root tip, when compared with those of Ophioglossum, show a very much greater regularity in the disposition of the cells. This is less marked in B. ternatum, and probably an examination of such forms as B. simplex will show an approximation to the condi- tion found in Ophioglossum, although Holle's figure of B. luna^ VII PTERIDOPHYTA—FILICINEJE—OPHIOGLOSSACEAi 267 ria shows even greater regularity in the arrangement of the apical meristem than is found in B. I iri^ijiicniiiin. A careful examination of this point is much to be desired. The first wall in the young lateral segment is the sextant wall, as in the higher Ferns, and divides the segment into two cells of unequal depth. The next wall divides the larger of these cells into an inner and an outer one, the former becoming the initial of the central plerome cylinder, the outer one, to- gether wnth the whole of the smaller semi-segment, giving rise to the cortex, in which the divisions are very similar to, but Fig. 147. — Tetrarch vascular bundle of the root of B. Virginianum, X85; en, endo- dermis; ph, phloem; x, xylem. somewhat less regular than in Equisehim and the leptospo- rangiate Ferns. As usual in roots of this type, segments are also cut off from the outer face of the apical cell, but I have never seen, either in B. Virginianum or B. tcrnatum, any indica- tion that the growth of the root-cap was due exclusively to the development of these segments, as Holle states both for B. lunaria and Ophioglossiim vidgatum. In both species of Botry- chiiini examined by me the growth of the root-cap was evidently due in part to the division of cells in the outer part of the lateral segments, so that in exactly median sections there w^as not the 268 MOSSES AND FERNS chap. clear separation of the root-cap from the body of the root that is so distinct in Equisetum, for example. The central cylinder of the root is bounded by an endoder- mis whose limits, however, are not so clearly defined as in the more specialised Ferns. The number of xylem and phloem masses varies, even in the same species. In B. Virginianum the larger roots show three or four xylem masses (Fig. 147). B. ternatum^ has usually a triarch bundle, while B. lunaria is commonly diarch (Holle (i), p. 245). The elements both of the xylem and phloem are much like those in the stem and do not need any special description. The roots increase consider- ably in diameter as they grow older, but this enlargement does not take place at the base, where the root is noticeably con- stricted. The enlargement is due entirely to the cortical tissue, and is mainly simply an enlargement of the cells. The diameter of the central cylinder remains the same after it is once formed. In the outer part of the root, as in the stem, there is a develop- ment of cork. The Sporangium In the simplest forms of B. simplex the sporangia, which are much larger than those of 5. Virginianum, form two rows very much as in Ophioglossum; but in all the more complicated forms the sporangiophore branches in much the same way as the sterile part of the leaf, and the ultimate segments become the sporangia. In B. Virginianum the development of the individual sporangia begins just about a year previous to their ripening, and if the plants are taken up about the time the spores are shed, the earliest stages may be found. The sporan- giophore is at this time thrice pinnate in the larger specimens, and an examination of its ultimate divisions will show the youngest recognisable sporangia. These form slight elevations growing smaller toward the end of the segment (Fig. 148), and exact median sections show that at the apex of the broadly conical prominence which is the first stage of the young sporan- giumi there is a large pyramidal cell with a truncate apex. Holtzman (i) thinks the sporangium may be traceable to a single cell, and that the divisions at first are like those in a three-sided apical cell. I was unable to satisfy myself on this * B. ternatum = B. obliquum (Underwood (5) p. 72). vii PTERIDOPHYTA—riLICINEAl—OPHIOGLOSSACEAl 269 point, but the youngest stages found by me in whicli the sporangial nature of the outgrowths was unmistakable, would not forbid such an interpretation, althougli there was no doubt that the basal part of the sporangium is derived in part from the surrounding tissue. From the central cell, by a periclinal wall, an inner cell, the archesporium, is separated from an outer one. The outer cell divides next by cross walls, and this is followed by similar divisions in the inner cells (Fig. 148). The succeeding divi- FiG. 148. — Botrychium Virginianum. Development of the sporangia. A, i, 2, Very young sporangia; B, a somewhat older one, X480; C, older sporangium, X240; all median longitudinal sections, the sporogenous cells are shaded. sions in the outer cells are now mainly periclinal, and transform the four cells lying immediately above the archesporium into as many rows of tabular cells. Growth is active in the mean- time in the basal part of the sporangium, which projects more and more until it becomes almost spherical. To judge from the account given by Goebel (3) and Bower (16) oi B. hinaria, this species corresponds closely in its early stages to B. Vir- ginianmn. The later divisions in the archesporium do not apparently follow any definite rule, but divisions take place in all directions until a very large number of cells is formed. 270 MOSSES AND FERNS chap. The cells immediately adjoining the sporogenous tissue divide into tabular cells, some of which contribute to the tapetum, which is to some extent, at least, derived from the outer cells of the sporogenous complex, as in Ophioglossum. (See also Goebel (22) p. 758). The sporangium shortly before the isolation of the spore mother cells (Fig. 148 C) is a nearly glob- ular body with a thick, very short stalk. The central part of the upper portion is occupied by the sporogenous tissue surrounded by a massive wall of several layers of cells. The central cells, as usual, have larger nuclei, and more granular contents than the outer ones. The stages between this and the ripe sporangium were not seen, so that it cannot be stated positively whether all the cells of the definitive sporogenous tissue (which seems probable) or only a part of them, as in Ophioglossum, develop spores. The wall of the ripe sporangium has 4-6 layers of cells, and sometimes the place of dehiscence is indicated, as in Ophio- glossum, by two rows of smaller cells (Fig. 148, C). The stalk is traversed by a short vascular bundle, which is first evident about the time that the number of sporogenous cells is complete, and joins directly with the young vascular bundle of the leaf segment (Fig. 148, C) . The ripe sporangium opens by a transverse slit, as in Ophioglossum. The presence of fungous filaments in the roots of the Ophioglossacese has been repeatedly observed, and has been the subject of recent investigations by Atkinson (2), who is inclined to regard them as of the same nature as the mycorhiza found in connection with the roots of many Dicotyledons, especially Cupuliferge. Atkinson asserts that he finds them invariably present in all the forms he has examined ; but Holle ( i ) states that, while they are usually present in Ophioglossum, he has found strong roots entirely free from them, and that in Botry- chium riitcrfolium they were mainly confined to the diarch roots, and that this is connected with a weakening of the growth of the root through the growth of the fungus, by which the triarch bundle of the normal fully-developed root is replaced by the. diarch form of the weaker one. Helminthostachys The third genus of the Ophioglossacese, Helminthostachys, with the single species H. Zeylanica, is in some respects inter- VII PTERIDOPHYTA-FILlCINEAi-OPHIOGLOSSACEJE 271 mediate between the other two, but differs from both in some particulars. The sporophyte has a creeping fleshy subterranean rhizome, with the insertion of the leaves corresponding to Opliio- glosswn pendulum. According to Prantl (7), who has made a somewhat careful study of a plant, the roots do not show any definite relation to the leaves, as Holle claims is the case in the other genera. The plant sends up a single leaf, which may reach a height of 30 to 40 cm. or more, and as in the Opliio- glossiim z'ulgatimi and B. V ir giniannm , the sporangiophore arises from the base of the sterile division of the leaf. Hie latter is ternately lobed, and the primary divisions are also divided again. The venation is different from that of the other Ophioglossacese, and is extremely like that of Angioptcris or Dancca. Each pinnule is traversed by a strong midrib, from which lateral dichotomously branched veins run to the margin. In regard to the structure of the sheath that encloses the young leaf and stem apex, Hehninthostachys resembles Bofrychiuni. The apex of the stem, as in the other genera, grows from a single initial cell. The stem has a single axial stele, with the form of a hollow cylinder, interrupted upon the upper side by the leaf-gaps. In the youngest stems, the stele is solid. There is an imperfect inner, and a distinct outer endodermis. The xylem is mesarch — i. e., it begins to develop in the center of the bundle — and its differentiation goes on very slowly. There is no formation of secondary wood as in the larger species of Botrychium. (Farmer (6)). The sieve-tubes have sieve-plates on their lateral faces, and similar sieve areas occur upon the walls of the adjacent phloem cells. The metaxylem has bordered pits, apparently similar to those of Botrychium Virginianum. The roots resemble those of Botrychium. There are from three to seven xylem masses. The sporangiophore is long-stalked and in general appear- ance intermediate between that of the other genera, but a careful examination shows that it is much more like that of Botrychium. It is pinnately branched, but in an irregular way, and the small branchlets bear crowded oval sporangia, which open longi- tudinally on the outer side, and not transversely as in the other genera. The tips of the branches, instead of forming sporangia as in Botrychium, develop into green leaf-like lobes, which upon the shorter branchlets are often arranged in a rosette of three or 272 MOSSES AND FERNS chap. four together, with the sporangia close below them (Fig. 141, D). This at first sight looks as if the sporangia were produced upon the lower side of these, like Equisetum, but a very slight examination shows at once that this is only apparent, and the sporangia are undoubtedly outgrowths of the branches as in Botrychium. The green lobes are seen to be only the vegetative tips of the branches, or perhaps better comparable to such sterile leaf segments as are not uncommon in Osmunda Claytoniana. (lower (17), Goebel (22), p. 664.) The sporangiophore in Helminthostachys originates as in the other genera, and is bent over and protected by the sterile leaf-segment, very much as in Botrychium. There is a certain correspondence between the early stages of the sporangiophore of Helminthostachys and that of Ophioglossum, but in the former there are later developed short lateral outgrowths, or secondary sporangiophores, which bear clusters of sporangia more like those of Botrychium, but the pinnate form of the sporangiophore is much less evident. The young sporangia project less than those of Botrychium, but otherwise closely resemble them. The archesporium is referable to a single mother-cell, but the tapetum is derived from the surrounding tissue, and not from the primary archesporium, as in Ophioglossum. Some of the sporogenous cells, as in Ophioglossum, become broken down. CHAPTER VIII MARATTIALES The Marattiace^ The Marattiacese, the sole existing family of the order, at the present time includes five known genera, with about twenty- five species of tropical and sub-tropical Ferns. Many fossil types are known which evidently were related to the Marat- tiacese, and they seem to comprise the majority of the Palaeo- zoic Ferns. Recently a good deal of attention has been paid to these Ferns, and our knowledge of their life-history and structure is fairly complete. Some of them are plants of gigantic size. Thus the stem of Angiopteris evecta is sometimes nearly a metre in height and almost as thick, with leaves 5 to 6 metres in length, and some species of Marattia are almost as large. The other genera, Kaiilfiissia, Archangiopteris and Dancca, include only species of small or medium size. While in the structure of the tissues and the character of the sporangia these show some resemblances to the Ophioglossacese, their general appearance is more like that of the true Ferns, with which they also agree in the circinate vernation of their leaves. The sporangia are borne upon the lower surface of ordinary leaves, as in most lepto- sporangiate Ferns, but the sporangia themselves are very differ- ent, and are more or less completely united into groups or synangia, which open either by longitudinal slits or, in Dancea, by a terminal pore. The base of the leaf is provided with a pair of fleshy stipules, which possibly correspond to the sheath at the base of the petiole in Botrychium. 18 273 274 MOSSES AND FERNS chap. The Gametophyte The germination of the spores and development of the prothalhum were first investigated by Luerssen (5) and Jonk- man (i) in Angiopteris and Marattiaj and later by the latter investigator for Kaulfussia (2). More recently Brebner (i) has described the prothallium and embryo in Dancea. The spores are of two kinds, bilateral and tetrahedral, but the former are more common. They contain no chlorophyll, but oil is present in drops of varying size, as well as other granular bodies. The nucleus occupies the centre of the spore and is connected with the wall by fine protoplasmic filaments. The wall of the spore is colourless and shows three coats, of which the outer one (perinium) is covered with fine tubercles. Germination begins within a few days and is first indicated by the development of chlorophyll. This does not, as Jonkman asserts, first appear in amorphous masses, but very small, faintly-tinted chromatophores are present between the large oil- drops, and rapidly increase in size and depth of colour as ger- mination proceeds, their number increasing by the ordinary division. In the bilateral spores the exospore is burst open above the thickened ventral ridge found in these spores, and the growing endospore slowly protrudes through this. The spore enlarges to several times its original diameter before the first division occurs, and forms a globular cell in which the large chloroplasts are arranged peripherally. The first division takes place about a month after the spores are sown, and is perpendicular to the longer axis of the cell, dividing it either into two equal parts, or the lower may be much smaller and develop into a rhizoid. In the former case each cell next divides by walls at right angles to the first, and the resulting cells are arranged like the quadrants of a circle, and one of these cells becomes the two-sided apical cell from which the young prothallium for a long time grows (Fig. 149), much as in Aneura. This type of prothallium, according to Jonkman, is commoner in Marattia than in Angiopteris^ where more com- monly a cell mass is the first result of germination. This latter is usually derived from the form where a rhizoid is developed at first. In this case only the larger of the primary cells gives rise to the prothallium. In the larger cell, divisions take place in three directions and transform it into a nearly globular cell VIII MARATTIALES '/o mass, terminated by four quadrant cells, one of which usually becomes the apical cell, much as in the flat prothallium. In exceptional cases the first divisions are in one plane and a short filament results. As soon as the apical cell is established it ^rows in precisely the same way as the similar cell in the tliallus of a Liverwort, and produces a thallus of much the same f(jrm and structure. As the prothallium grows older, however, a cross-wall forms in Fig. 149. — Angiopteris evecta. Germination of the spores, — A, B, X220; C, X175; sp, spore membrane; x, apical cell (after Jonkman), the apical cell, and this is followed by a longitudinal wall in the outer one, forming two similar cells wdiich, by further longi- tudinal divisions, may produce a row of marginal initials, and the subsequent growth of the prothallium is due to the divisions and growth of this group of initial cells (Fig. 150, A). At first the prothallium has a spatulate form, but before the single apical cell is replaced by the group of marginal initials, the outer cells of the segments grow more rapidly than the inner ones, and the segments project beyond the apical cell, 276 MOSSES AND FERNS CHAP. which comes to lie in a depression between the two lobes formed by the outer parts of the segments, and the prothallium assumes the heart-shape found in most homosporous Ferns. The sec- ondary initial cells vary in number with the width of the inden- tation in which they lie. Seen from the surface they are oblong in shape, but in vertical section are nearly semicircular (Fig. 150, B). Basal segments are cut off by a wall that extends the whole depth of the prothallium, and the segment is then divided by a horizontal wall into a dorsal and ventral cell of nearly equal size. The divisions are more numerous in the ventral than in the dorsal cells of the segment, this difference first being mani- fest some distance back of the apex. Owing to this, a strongly projecting, nearly hemispherical cushion - like mass of tissue is formed upon the ventral surface. The superficial cells of both sides of the prothallium have a well-marked cuticle. Nu- merous brown rhizoids, which, like those of the sim- pler Liverworts, are uni- cellular and thin - walled, grow out from the cells of the lower surface, especially from the broad midrib. The full-grown prothallium in M. Douglasii is sometimes a centimetre or more in length (Fig. 151), and tapers from the broad heart-shaped forward end to a narrow base. In Angiopteris (Farmer (3) ) it is more nearly orbicular. In both genera it is dark-green in colour, looking very much like the thallus of Anthoceros IcBvis, and like this too is thick and fleshy in texture. A broad midrib extends for nearly the whole length of the thallus and merges gradually into the wings, which are also several-layered, nearly or quite to the margin. The prothallium of Dancea (Brebner (i)) resembles more Fig. 150. — Marattia Douglasii. A, Horizon- tal section of prothallium apex, with two initials, Xi6o. B, Longitudinal section of a similar growing point; d, dorsal; v, ventral segment. VIII MARATTIALES 277 closely that of Angiopteris, than that of Marattia. The rhizoids are miilticeHular, recalhn^ those of the ^ametophyte of Botrychinm. The very old prothalHa sometimes hranch dichotomously (Fig. 151, B, C), and the process is identical with tliat in the thallose Hepatic?e. The two growing points are separated by a median lobe in the same way, and the midrib with the sexual B X. . .1 ■>•.•.-■ ..• Fig. 151. — Marattia Douglasiu A, Prothallium about one year old, X2; B, the same prothallium about a year later, showing a dichotomy of the growing point; C, the same seen from below, showing two archegonial cushions (^) ; D, prothallium with young sporophyte, X4; E, a somewhat older one, seen from the side; r, the pri- mary root. organs upon It forks with it, exactly as we find, for example, the antheridial receptacle forking in Fimbriaria Californica (Fig. I, A). Besides this form of branching, which is not common, adventitious buds are produced upon the margin of the thallus very frequently. These grow^ in precisely the same way as the main prothallium, and after a time may become 278 MOSSES AND FERNS chap. detached and form independent plants; or they may develop sexual organs (mainly antheridia) while still connected with the mother plant. The duration of the prothallium is apparently unlimited, so long as it remains unfecundated. The writer kept prothallia of Marattia Douglasii for nearly two years, during which they grew continuously and finally reached a length of over two centimetres. At the end of this time they were growing vigorously, and there was nothing to indicate the slightest decrease in their vitality. The prothallia are monoecious, although not infrequently the smaller ones bear only antheridia. The latter always appear first, and are mainly found upon the lower side of the midrib, but may also occur upon the upper side. The arche- gonia are confined to the lower surface of the midrib, and as they turn dark brown if they are not fertilised, they are visible to the naked eye as dark brown specks studding the broad thick midrib. Both antheridia and archegonia resemble closely those of Ophioglossiim. The Sex-organs The antheridium arises from a single superficial cell which first divides into an inner cell, from which the sperm cells are derived, and an outer cover cell (Fig. 152, A). The latter divides by several curved vertical walls (Figs. E-G) which intersect, and the last wall cuts off a small triangular cell (0), which is thrown off when the antheridium opens, and leaves an opening through w^hich the sperm cells are ejected. The inner cell, by repeated bipartitions, gives rise to a large number of polyhedral sperm cells. Before the full number of these is complete, cells are cut off from the adjacent prothallial cells, which completely enclose the mass of sperm cells. As in other Archegoniates, the nucleus of the sperm cell, after its final division, shows no nucleolus. The first sign of the formation of the spermatozoid that could be detected was an indentation upon one side, followed by a rapid flattening and growth of the whole nucleus. The cytoplasmic prominence which, according to Strasburger, is the first indication of the formation of the spermatozoid, could not be certainly detected. The main part of the spermatozoid, stains strongly with alum-cochineal, and is sharply differentiated against the colourless cytoplasm, and VIII MARATTIALES 279 for some time shows the characteristic nuclear structure. The origin of the ciha was not clearly made out, but there is little question that they arise from a blepharoplast as in (jther cases that have been more recently investigated. The free sperma- tozoid (Fig. 152, I), is a flattened band, somewhat blunt behind and tapering to a fine point in front; attached to a point just back of the apex are several fine cilia. The body shows only about two complete coils. Fig. 152. — Marattia DouglasU. Development of the antheridium. A-D, Longitudinal section, X515; E-G, surface views, X257; H, ripe sperm cells; I, free spermato- zoids, X1030; 0, operculum. The youngest archegonia are met w^ith some distance back of the growing point, and apparently any superficial cell is potentially an archegonium mother cell. The latter divides usually into three superimposed cells (Fig. 153, A), of which the lowest (b) forms the base of the archegonium. The basal cell, however, may be absent in Marattia Douglasii, as is also the case in Angiopteris and Dancea. From the middle cell by a transverse division are formed the primary neck canal cell and 280 MOSSES AND FERNS CHAP. the central cell. Each of these divides again transversely. In the upper one this division is often incomplete and confined to the nucleus; but in the central cell the division results in the separation of the ventral canal cell from the ovum. Before the separation of the primary neck canal cell from the central cell, the cover cell divides as in the Liverworts into four cells by intersecting vertical walls, and each of these cells by further obliquely transverse walls forms a row of about three cells, and these four rows compose the short neck. The canal cells are Fig. 153. — Marattia Douglasii. A-D, Development of the archegonium, X4S0; E, sec- tion of the fertilised egg, showing the spermatozoid (sp) in contact with its nu- cleus, X485; F, successive longitudinal sections of a young embryo, X225; b, b, the basal wall; the arrow points towards the archegonium. very broad and the ^gg cell small, so that after the archegonium opens it occupies but a small part of the cavity left by the disintegration and expulsion of the canal cells. Before the archegonium is mature, flat cells are cut off from the adjacent prothallial tissue as in the antheridium (Fig. 153, D). The neck of the ripe archegonium projects but little above the surface of the prothallium, and in this respect recalls both the lower Ophioglossaceae and the Anthocerotes. The ripe ovum is somewhat elliptical, and slightly flattened vertically. Its VIII MARATTIALES 281 upper third is colourless and nearly hyaline. This is the ''receptive spot," and it is here that the spermatozoid enters. The nucleus is of moderate size, and not rich in chromatin; a small but distinct nucleolus is present. The spermatozoid retains its original form after it first enters the egg, and until it comes in contact with the membrane of the egg nucleus. It afterwards contracts and assumes much the ap])earance of the nucleus of the sperm cell previous to the differentiation of the spermatozoid. The two nuclei then gradually fuse, but all the different stages could not be traced. Before the first division A. Fig. tftA'-^-Marattia Douglasii. Embryogeny. A, Longitudinal; B, transverse sections of embryos, X215; C, vertical section of an older embryo, showing its position in the prothallium, X72; st, the stem; pr, prothallium; D, upper part of the same embryo, X215. takes place, however, but one nucleus can be seen, and this much resembles the nucleus of the unfertilised egg. It is prob- able that the nucleus of the spermatozoid really penetrates the cavity of the egg-nucleus as has been shown to be the case in Onoclea. ( See Shaw ( i ) ) . The Embryo — (Farmer (3) ; Jonkman (s)) After fertilisation the egg enlarges to several times its original size before dividing. The first (basal) wall is trans- 282 MOSSES AND FERNS CHAP. verse and is followed in each half by two others, the median and octant walls. The nearly globular embryo is thus divided into eight similar cells, each having the tetrahedral form of a globe octant. The next divisions are not perfectly understood, and evidently are not absolutely uniform in all cases. All the octants at first show nearly uniform growth, and the embryo retains its nearly oval form (Figs. 153, F, 154, A). The first division in the octants is essentially the same, and consists in a series of anticlinal walls, before any periclinal walls appear, so that we may say that for a short time each octant has a distinct apical growth, and there are eight growing points. The older Fig. 155. — Marattia Douglasii. A, Cross-section of the young sporophyte at the junc- tion of the cotyledon and stem; st, the apical meristem of the stem, X215; B, the stem apex of the same, X430; C, longitudinal section of the stem apex of a plant of about the same age, X21.S; tr, the primary tracheary tissue; r^, the second root. embryo shows an external differentiation into the first leaf, stem, and root, but the foot is not clearly limited at first. The basal wall separates the embryo into two regions, epibasal and hypobasal. From the former the cotyledon and stem apex are derived, from the latter the root and foot. The cotyledon arises from the anterior pair of epibasal octants, which are in the Marattiacege, unlike all the other Ferns, turned away from the archegonium opening. In the earliest stages where the cotyledon is recognisable, no single apical cell could be made out, and later the growth is very largely basal. Vlll MARATTIALES 283 At first the growth is nearly vertical, but it soon becomes stronger upon the outer side, and the leaf rufliment bends inwards. At this stage the dififerent tissues begin to l>e dis- tinguishable. Somewhat later the tip of the cotyledon becomes flattened, and still later there is a dichotomy of this flattened part which thus forms a fan-shaped lamina (Fig. 157). The Fig. 156. — Marattia Douglasii. A, B, C, Three transverse sections of a root from the young sporophyte; A shows the apical cell (x), X215; D, longitudinal section of a similar root, X260; E, vascular bundle of the root, X260. first tissue to be recognised is the vascular bundle w^hich traverses the centre of the petiole and at first consists of uni- form thin-walled elongated cells (procambium). This forma- tion of procambium begins in the centre of the embryo and proceeds in three directions, one of the strands going into the 284 MOSSES AND FERNS chap. cotyledon, one in an almost opposite direction to the primary root, and a very much shorter one to the young stem apex, which lies close to the base of the cotyledon. The outer layer of cells of the cotyledon forms a pretty clearly defined epidermis separated from the axial procambium strand by several layers of young ground-tissue cells. The apex of the young stem is occupied in some cases, at least, by a single apical cell, which probably is to be traced back directly to one of the original octants of the embryo. Whether this is always the case in the youngest stages cannot be de- termined until further investigations are made. Farmer (3) was unable to make out a single initial in Angiopteris, which otherwise agrees closely with Marattia. Dancea, according to Brebner ( i ) , shows a single initial cell at the stem-apex, as well as that of the primary root. The study of the root was confined mainly to the older embryos, and although some variation is noticed, it is pretty certain that there is a single apical cell, not unlike that found in the Ophioglossacese. Whether this can be traced back to one of the primary hypobasal octants, it is impossible now to say; but Farmer's statement that in Angiopteris there is at first a three-sided apical cell would point to this. Unfortunately my own preparations of Marattia were too incomplete to decide this point in the latter. In the older root the form of the apical cell was usually a four-sided prism, from all of whose faces segments were cut off, although sometimes an approach to the triangular form found in the Ophioglossacese was observed. The foot is much less prominent than in Botrychium, and in this respect the Marattiacese are more like Ophioglossum (Mettenius (2), PL xxx). In Marattia all the superficial cells of the central region of the embryo become enlarged and act as absorbent cells for the nourishment of the growing embryo. As the embryo grows, the surrounding prothallial tissue divides rapidly, and a massive calyptra is formed which com- pletely encloses the young sporophyte for a long time. Owing to the position of the cotyledon and stem, which grow up vertically through the prothallium, a conspicuous elevation is formed upon its upper side, through which the cotyledon finally breaks, A similar elevation is formed by the calyptra upon the lower side, through which the root finally penetrates, but not until after the cotyledon has nearly reached its full development. VIII MARATTIALES" 285 The proihallium does not die immediately after the young sporophyte becomes independent, but may remain aHve for several months afterwards, much as in Botrychiiim. The first tracheary tissue arises at the junction of the bun- dles of the cotyledon, stem, and root. These primary tracheids are short and their walls are marked with reticulate thickeninj:j^s. From this point the development of the tracheary tissue, as well as the other elements of the bundles, proceeds toward tlie a])ices of the young organs. The formation of the secondary tracheids is always centripetal. Fig. 157. — A, Young sporophyte of Danaea simplicifolia, still attached to the gameto phyte, pr; X3; B, an older sporophyte of the same species; C, gametophyte of Angiopteris evecta, with the young sporophyte. (A, B, after Brebner; C, after Farmer.) Jeffrey (3) states that in the young sporophyte of several species of Dancea examined by him, the stele has the form of a tube with both internal and external endodermis and phloem. Both internal endodermis and phloem tend to disappear in the later-formed part of the stem. The tubular central cylinder is interrupted by the foliar gaps, and later there are formed medullary vascular strands, and the vascular system gradually assumes the very complicated form met with in the older sporophyte. Brebner (3) states that in Dancea simplicifolia the 286 MOSSES AND FERNS chap. primary vascular axis is a .simple concentric stele, which is later replaced by a cylindrical stele like that of D. alata. Short hairs with cells rich in tannin, and staining strongly with Bismarck-brown, occur sparingly upon the leaves and stem of the young sporophyte. The fully-developed cotyledon has the fan-shaped lamina somewhat lobed, and the two primary veins arising from the for