eee ee seen ALBERT K. MANN LIBRARY AT CORNELL UNIVERSITY CORNELL UNIVERSITY LIBRARY All books are subject to recall after two weeks DATE DUE Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924087302018 THE STRUCTURE AND DEVELOPMENT OF MOSSES AND FERNS Oc The Structure and Development of Mosses and Ferns (Archegoniatae) THIRD EDITION, REVISED AND ENLARGED BY DOUGLAS HOUGHTON CAMPBELL, Pu.D. PROFESSOR OF BOTANY IN THE LELAND STANFORD JUNIOR UNIVERSITY jpewo Pork THE MACMILLAN COMPANY Lonpon: MACMILLAN & Co., LTD. 1918 All rights reserved Copyricut, 1905 By THE MACMILLAN COMPANY — Set up and electrotyped Published, September, 1905 Reprinted July, 1913 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 Archegoniate 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. Vv 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. 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. vii CONTENTS CHAPTER I ENTRODUCTION 6:36.40 oie sexesiawerdwsitie aise Beene ee aes 00 aio tiorsavetceateeares: (\oE CHAPTER II MuSCINEZ (BrYOPHYTA)—HEPATICE—MARCHANTIALES secceceeecoes 8 CHAPTER III THE JUNGERMANNIALES 424 sc.s.c4 80a cccu.seesewiew vei es sos store erelasins 72 CHAPTER IV THE ANTHOCEROTES 22.0.0... eeeceeececeecoereeeseecees stnsa.giavacevelvieres 120 CHAPTER V Tue Mosses (Musci): SPHAGNALES—ANDREEALES. esseesesccececce 160 CHAPTER VI THE: BRYALES: sitscosnwasd tic tore de hs oss CaN GRAS ROT RAN EE aE Bes 188 CHAPTER VII THE PTERIDOPHYTA—FILICINEE—OPHIOGLOSSACE .sescccscscecececs 229 CHAPTER VIII MEARATTIAUESS | Ssv5 shoes wise stodeaieceleatn aw idee eriealw giv ao ats era g epee eee 273 CHAPTER IX FriuictinE& LrepTosPpoRANGIATE .......... ate Heda ws < aislelonvaletnekeaa eee 305 CHAPTER X THE Homosporous LEPTOSPORANGIATA (FILICES)......cececececeseces 346 CHAPTER XI LEPTOSPORANGIATZ HETEROSPOREZ (HYDROPTERIDES).....eceesceeseens 3096 CHAPTER XII EQUISETINEAS ¢ sie'es's age saat iid dane cui and ugiiens x 302844 94 GRO TSS 443 CHAPTER XIII ISVCOPODINER: gies 050 o3'6 505.03 eesti acide gee Pha tiene Bee MOS bose Save 483 CHAPTER XIV WSOETACER: 2.c3s:36.¢ sv scien sr acnangndgsenw erated toes enaiauees wi eeRas 536 CHAPTER XV Tue NATURE OF THE ALTERNATION OF GENERATIONS. ...-.0000eeeeeeuee 562 CHAPTER XVI Fossit: ARCHEGONIATES, ::acvsisccusenguscumbosbqewnebe ce geen sceagars 576 CHAPTER XVII SUMMARY AND CONCLUSIONS. ...... 0c. cece cee c ee cee cece ee seeaeeeecs 592 CONTENTS CHAPTER I INTRODUCTION UNpER the name Archegoniate 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 Gymnospermz or Archesperme might very properly be also embraced here, but we shall use the term in its more restricted meaning. The term Archegoniate 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 lowest forms the egg. The others become more or less completely disorganized and are discharged from the archegonium at maturity. Among the Algz there is no form at present known in which the female organ can be certainly compared to the archegonium, although the oogonium of the Characez recalls it in some respects. The antheridium or male organ of the Archegoniate, 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 Algz, especially the Characee. 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 1 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 Archegoniate, and differs mainly from the same process in the higher green Algz, especially the Characee, 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 Algz, and point unmistakably to the origin of the Arche- goniate from similar aquatic forms. Indeed all of the Archegoniate 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 gemmez, 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 Alge, 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 Marchantiacee, 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 egg, 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 with 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, which 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; while 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 Io to 15 metres in height, with leaves 5 to 6 metres in length. In the formation of the spores all of the Archegoniatz 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 Osmunda, 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 Marattiacee and Equisetacee, 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 Marattiacez 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 moncecious, but in the more specialised ones are markedly dicecious. 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 Marsiliacez, 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, If MUSCINAE (BRYOPHYTA)—HEPATICAE—MARCHANTIALES THE first division of the Archegoniate, the Muscinez or Bryophyta, comprises the three classes, Hepaticee 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, 7. e., Riella and Ricciocarpus among the Hepat- ice, 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., Buxbaumia, the game- tophyte of the Muscinez is abundantly supplied with chloro- 8 CH. II MUSCINEZZE—HEPATIC E—MARCHANTIALES 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 Hepaticz, like Aneura and Pellia, it is a flat, usually dichoto- mously branched thallus composed of nearly or quite uniform cells, without traces of leaves or other special organs. From this simplest type, which is quite like certain Alge, 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 Marchantiacez. 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 Hepatice, but in the foliose Hepaticze and Mosses is with few exceptions a three-sided pyramid. The gametophyte of the Muscinez frequently is capable of rapid multiplication, which 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 away of the tissues behind them, so that each growing tip becomes the apex of a new plant. Very common in the Hepaticz, but less so in the Mosses, is the formation of gemme 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 multifida they are formed within the cells and discharged in a manner that seems to be identical with that of the zoospores of many Algz. Again, multicellu- lar gemme of peculiar form occur in several of the Hepatice, e.g., Blasia, Marchantia, where they occur in special receptacles, / Io MOSSES AND FERNS CHAP. and among the Mosses similar ones are common in Tetraphis and some other genera. The archegonia of all the Muscinee 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 egg, 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 Muscinez 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 Hepatice. The most marked difference, however, between the arche- gonium of the Hepatic 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 MUSCINEZ—HEPATICZ—MARCHANTIALES 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.¢., 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 egg, 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 egg, where it fuses with the egg-nucleus, and thus effects fertilisation. The egg 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 Hepaticze 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 Hepatice 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 are usually placed singly in the axils-of more or less modified leaves, but in most Mosses the antheridia form a terminal group. Mixed with the sexual organs are often found sterile hair-like organs, paraphyses, often of very characteristic forms. In the foliose Hepaticze and most Mosses, the archegonia are often surrounded by specially modified leaves, and in the former there is also an inner cup-like perichetium formed from the tissue surrounding 12 MOSSES AND FERNS cHar. the archegonia. In the thallose Hepatic, both antheridia and archegonia are generally enclosed by a sort of capsule, similar to the perichetium of the foliose forms formed by the growth of the tissue of the thallus immediately surrounding them. Tue ASEXUAL GENERATION (Sporophyte, Sporophore, Sporogonium) The sporophyte of the Muscinee 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 Hepaticz, 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 Spherocarpus, or more commonly assume the form of elongated cells,—elaters, which assist in scattering the ripe spores. CLASSIFICATION Crass I. Hepatice (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- bryum, strongly dorsiventral, 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 (Aneura multifida) or gemme—(many foliose Jungermanniacee, 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 MUSCINE Zi—HEP ATIC4—MARCHANTIALES 13 Crass II. Anthocerotes. Gametophyte, a simple thallus, or sometimes showing a trace of leaf-formation in Dendroceros; 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. Crass III. Musci (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 which 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 gemmez. Both stem and leaves have the tissues more highly differentiated than is the case in the Hepatice. The archesporium is developed as a rule later than is the case in the Hepaticz, 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 HEPATICA The Hepatice 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. Hepaticze 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 Hepatic approach the Algze, the thallus of the simpler forms being but little more compli- cated than that of many of the higher green Alge. 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, ¢. g., Riccia, is very much like the spore-fruit of Coleochete, one of the confervoid green Algz; 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 Hepatic is found in the thallose Jungermanniacez 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 Marchantiacee, 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- cee (Fig. 16) this is carried still further, and the air-chambers often assume a definite form, and a distinct epidermis with characteristic pores is formed. In the Marchantiacee also ventral scales or leaf-like lamellze are developed, and rhizoids of two kinds are present. Starting again from the flat, simple thallus of Ancura there has been developed the leafy axis of the more specialised Jungermanniacez. Between the latter and the strictly thallose forms are a number of interesting inter- mediate forms, like Blasia and Fossombronia, 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 MUSCINEZ—HEP ATIC4Z—MARCHANTIALES 15 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 (Marchantia) or rows of cells (Cono- cephalus) 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., Marchantiacee, 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 Jungermanniacez, however, 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 Jungermanniacee 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, Spherocarpus (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- vicina (Fig. 38), separated by spaces where no archegonia are found. Here each group of archegonia has a common invol- ucre. In Aneura and most of the higher Marchantiacez the archegonia are found in the same way, but upon special modi- fied branches. In the foliose Jungermanniaceze the origin of the archegonia is somewhat different. Here they are formed upon short branches, where, after a small number of pericheetial leaves have been formed, the subsequent segments of the apical 16 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 Jungermanniaceze 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., Fimbriaria). In the foliose Junger- manniacez 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- tiacee, Spherocarpus) or vertical (Jungermanniacez). II MUSCINEZ—HEP ATIC —MARCHANTIALES 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 Hepaticz 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 (1), Buchtien (1), and others of late years, as well as by many of the earlier observers, and a comparison with other Hepatice 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 Liverworts. 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 ((1), 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 ((1), 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 Ricciacee and in Spherocarpus new archegonia continue to form even after several have been fertilised, so that numerous sporogonia develop upon the same branch of the 2 18 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 Spherocarpus (Fig. 30), which may be taken to represent the next stage of develop- ment, we notice two 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 Hepatic 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 Hepaticze except the lowest ones. The dehiscence of the sporogonium is different in the different orders. In the Ricciaceze and some Marchantiaceze the ripe sporogonium opens irregularly ; in a few cases (species of Fimbriaria) the top of the capsule comes off as a lid; iz II MUSCINEZ—HEPATICZ—MARCHANTIALES 19 most Jungermanniales the wall of the capsule splits vertically into four valves. The spores are always of the tetrahedral type, 1.¢., 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, ete. 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- manniacez, have also numerous chloroplasts, but these are lack- ing usually in those forms that require a period of rest before germination. In Pellia and Conocephalus 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 Hepatic 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 Schiffner ((1), p. 5): Orver 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 MUSCINEZ—HEPATICA—MARCHANTIALES 21 Fam. t. Ricciacee 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. Corsiniacee. 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. Marchantiacee. Air-chambers usually highly developed, and the chambers often containing a loose filamentous assimilative tissue. Pores upon the dorsal surface always present (except in Dumortiera 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 well 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 Ricciacez 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 Marchantiacez and Ricciaceze 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 Dumortiera and Conocephalus. 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, Fic. 1.—Marchantiales. A, B, Male plants of Fimbriaria Californica. A, from above; B, from below; (, antheridial receptacle; /, ventral lamelle, <4; C, Riccia glauca, X6; sp, sporogonia; D, Conocephalus conicus, X4; E, Targionia hypophylla, X2; ¢) antheridial branch. e.g., Targionia (Fig. 1, E), may fork comparatively seldom, and the new branches are for the most part lateral. The thallus II MUSCINEZ—HEPATICZ—MARCHANTIALES 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 Monoclea, and these spaces are either simple narrow canals, as in Riccia glauca, 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 Marchantiacez. The growth 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 lamellz 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 well-known gemmz 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, ¢.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 Californica, 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 RICCIACEE As a type of the simplest of the Marchantiacee, we may take the genus Riccia, represented, according to Schiffner ((1), 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. fluitans, 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, +). 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 lamellz 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 Ir MUSCINE4—HEPATIC4—MARCHANTIALES 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, 525. A, Vertical section through the growing point; +, apical cell; ar, young archegonium; JI, ventral lamelle; 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 growing 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 papille 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. Bischoffii). 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, 525; C, Xabout 260. C shows the dichotomy of the growing point; +, +’, 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 lamelle, 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 II MUSCINEZZ—HEPATICZA—MARCHANTIALES 27 are often scarcely to be detected except close to the growing point. In the case of Ricciocarpus 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. fluitans (Leitgeb (7), iv. p. 11) and R. erystallina 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. Inthe 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, with only a smail 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 lamella. These two species also show some difference as to the ventral scales. Those of R. fuitans are small and do not become separated into two, and in R. crystallina they are wanting entirely. Most of the Ricciacee multiply by special adventive shoots that arise from the ventral surface of the midrib. These become detached and form new individuals. According to Fellner (1) 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 Marchantiacee. 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 lamellz 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 MUSCINE42—HEP ATIC 4—MARCHANTIALES 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, 1). 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 celis 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 (1), always into four in FR. Bischoffii, and the same seems to be true for R. tricho- 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 Fic. 4.—A, Archegonium of Riccia trichocarpa, showing the ventral canal cell (v), 525; B, ripe archegonium of R. glauca, longitudinal section, 260. separates the ventral canal cell from the egg. 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. Bischoff. 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) II MUSCINE42—HEPATICA—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 egg. The cytoplasm is filled with gtanules, 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 1s 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 32 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 B Fie. 5.—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, 150; I, X600, the others X 300. 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 pcm MUSCINEAZ—HEPATICZ—M ARCHANTIALES 33 uppermost cells are often, although 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, 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 egg develops at once a cell-membrane and enlarges until it completely fills the cavity of the venter. The first division wall is more or less inclined to the axis of the archegonium, but approaches usually the horizontal. The lower of the two 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 IT 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 walls 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 SSiecsen Fic. 6.—A, B, Young embryos of R. glauca in longitudinal section, showing the venter of the archegonium, Xz260; 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 MUSCINEZ—HEP ATIC E—MARCHANTIALES 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- Fic. 7.—Riccia trichocarpa. A, Section of a spore mother cell undergoing its first division, X600; B, section of young spore tetrad, 300; C, section of ripe spore, X300; D, surface view of the exospore of a similar stage, X 300. selves at equal distances from each other, the division walls 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 microtome 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 Ricciaceze was only known in R. glauca (Fellner (1) ). 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 1I MUSCINEZ—HEP ATIC Z—MARCHANTIALES 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 A. Fic. 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. Fic. 9.—Riccia trichocarpa. Later stages of germination. A, from below, 260; B, optical section of A, showing apical cell 4, X520; C, X85; 7, 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 MUSCINEZA—HEPATIC4—MARCHANTIALES 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 papillz, 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 papillze, which are cut off 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 lamellz, which are quite absent from the young plant. CLASSIFICATION OF THE RICCIACEE 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-wide distribution. It is a floating form, like Riccia Auitans. Leitgeb ((7), vol. iv.) has made a very careful study of the structure and development of the thallus, which 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 Marchantiacee. 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 Marchantiacee 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. 10). 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 2 same as in Riccia. Garber (1), who has recently studied the development of Riccio- carpus, finds that it is not dicecious, as has been frequently asserted, Fic. 10.—Ricciocarpus natans. A, but rather proterandrous—that is, phe Pe B, terrestrial numerous antheridia are formed, ee but 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 (Oxymitra), represented by the single species, T. pyranidata, is much less widely distributed, belonging mainly to Southern Europe, but also found in Para- il MUSCINEZ—HEPATICZ—MARCHANTIALES 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 Ricciaceze and the Marchantiacez. 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, however, 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, Cronisia, represented also by a single species, C. paradoxa, is placed provisionally with the Ricciacee by Schiffner ((1), 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 Corsiniez, and forms a direct transition from the Ricciacez to that family.” THE CorSINIACEEH (Schiffner (1), p. 26). The family Corsiniaceze comprises but two genera, Corsinia and Funicularia (Boschia). Each genus contains but a single known species. Structurally they are intermediate in character between the Ricciaceze and Marchantiacee. Corsinia differs from all the higher Marchantiacez 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 which 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 Marchantiacez, 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- chantiacez. MarRCHANTIACEZ. Comparing the Marchantiacez with the Ricciacez, 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 Dumortiera and Monoclea, where the develop- ment of the air-chambers is partially or completely suppressed. The genera Ricciocarpus and Tessalina on the one hand, and Corsinia and Boschia on the other, connect perfectly Riccia with the Marchantiacee as regards the structure of air-spaces and epidermis, as they do in other respects. The epidermal pores in the Marchantiacez are sometimes simple pores sur- rounded by more or less symmetrically arranged guard cells (Fig. 11, 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. 11, C). There is a good deal of difference in the character of the air- chambers in different genera. In Reboulia and Fimbriaria, for instance, they resemble a good deal those of Ricciocarpus, a more or less complete division of the primary chambers being produced by the formation of diaphragms or laminz, 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. 18), 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. 1, 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 it MUSCINE4:—HEPATIC4—M ARCHANTIALES 43 in two rows. Leitgeb ((7), iv., p. 17), recognises two types of these organs. In their earliest stages they are alike, and both arise from papille close to the growing point. In both cases this papilla. is cut off from a basal cell, but in the first type (Sauteria, 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. Fic. 11.—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 (1) 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. 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 Hepatice, have been carefully studied by Pfeffer (2). The oil body has a round or oval form usually, and in the Mar- chantiez 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 Lunularia, less so in Marchantia and Preissia(Cavers(6) ; Kiister (1) ). The thallus of the Marchantiacee is made up al- Qc most entirely of parenchyma, but Goebel (3) fo) states that in Preissia commutata 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 Marchantiacez have no special non- sexual reproductive organs, but in the genera Fig. 12.—Mar- 5 . chantia poly. Marchantia and Lunularia special gemme are pro- morpha. duced in enormous numbers; and in the latter Part of a c e . tuberculate fOrm, which is extremely common in greenhouses, rhizoid, the plant multiplies only by gemmz, as the plants nee are apparently all female. These gemme, 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 gemme 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. {I MUSCINEZ—HEPATIC—MARCHANTIALES 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 Fic. 13.—Marchantia polymorpha. A, Plant with gemma cups (k, k), X2; B-F, development of the gemmz, 525; 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 IT, 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 gemmz 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, which secrete a mucilage that swells up when wet, and finally tears away the gemmee from their single-celled pedicels. The further development of the gemmez 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. 1, 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 Ricciacez, 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 Corsiniez (Leitgeb (7), vol. iv.), where the main distinc- tion between them and the lower Ricciacez 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 Marchantiez, 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 MUSCINEZZ—HEPATICA—MARCHANTIALES 47 antheridial receptacles are sometimes stalked, but more com- monly are sessile, and often differ but little from those of the higher Ricciacee. The sporogonium shows an ‘advance upon that of the Ricciacez 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 Corsinieze have the form of elaters. At maturity, also, the ripe capsule breaks through the calyptra, except in the Corsiniez, where, 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 Jungermanniacez, 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 wall. 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 Marchantiee is very much like that of Riccia. In.Fimbriaria Californica (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 lamellz 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 lacune in the dorsal part of the thallus begins earlier than in Riccia, and corresponds very closely to what obtains in Ricctocarpus. 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. 18, 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, 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 lacune are formed much as in Fimbriaria, 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 Fic. 14.—Fimbriaria Californica. A, Vertical sec- the compact colourless tion through the apex of a sterile shoot, show- tissue lying below it, and ng Satin tte acter 7-8 the cells form short con- an older part of the thallus, cutting througha fervoid filaments more te 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 Marchantiez 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) II MUSCINEZ—HEPATIC4Z—MARCHANTIALES 49 investigated D. irrigua, whose thallus is characterised by a peculiar areolation composed of projecting cell plates, 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. He had only herba- rium material to work with, but in this he detected traces of the epidermis and pores in the younger parts. I examined with some care fresh material of D. trichocephala, from the Hawa- iian Islands, and find that in this species, which has a perfectly 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- tiaceze, and the succession of segments the same, but no indi- cations of lacunz can be seen either near the apex or farther back, the whole thallus being composed of a perfectly contin- uous tissue without any intercellular spaces, and no distinct limit between the chlorophyll-bearing and the colourless tissue. As Dumortiera corresponds in its fructification with the higher Marchantiex, the peculiarities of the thallus are probably to 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 Marchantiaceous thallus and the other extreme found in D. trichocephala. Sexual Organs The structure and development of the sexual organs are very uniform among the Marchantiacee. In Fimbriaria Cali- fornica, which is dicecious, the antheridial receptacle forms a thickened oval disc just back of the apex. Not infrequently (Fig. 1, 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 papillz 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 4 50 MOSSES AND FERNS citab. cell are somewhat irregular, but more numerous than in Riccia, - so that the stalk of the ripe antheridium is more massive (Fig. 16). 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 Fimbriaria (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 Fic, 15.—Fimbriaria sp. (?). A, Part of a vertical section of a young antheiidial receptacle, showing two very young antheridia (g), 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 wall 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 Fimbriaria 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., Pl. x., Fig. 12) is repre- II MUSCINEZ—HEPATICZ—MARCHANTIALES 51 sented asempty. 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 about one and a half com- plete turns of a spiral. The cilia are very long, and the vesicle usually plainly evident. According to Ikeno (4), in Marchantia polymorpha the final division, resulting in the pair of spermatids, is unaccom- panied by a division wall, and this seems also to be the case in Fic. 16.—Fimbriaria Californica. A. Longitudinal section of a fully-developed male receptacle, 8; B, longitudinal section of a nearly ripe antheridium, X100; C, young sperm cells, X600; D, spermatozoids, X 1200. Fimbriaria. In the earlier divisions of the sperm-cells, each cell shows two centrosomes (Fig. 17, 1), 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. Fic. 17.—Marchantia polymorpha. Development of the spermatozoid, 1, Sperm-cells from the young antheridium; z, 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 Il MUSCINEZE—HEPATICZ—MARCHANTIALES 53 specialised forms are found in the genus JJarchantia and its allies, where the antheridial receptacle is borne upon a long stalk, which is a continuation of the branch from which it grows, and the receptacle is a branch-system. The growing point of the young antheridial branch forks while still very young, and this is repeated in quick succession, so that there results a round disc with a scalloped margin, each indentation marking a growing point, and the whole structure being equiva- lent to such a branch system as is found in Riccia or Anthoceros, where the whole thallus has a similar rosette-like form. The antheridia are arranged in radiating rows, the youngest one nearest the margin and the eldest in the centre. In some tropical species, e.g., MM. 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 Fimbriaria Californica, Peirce (1) 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 walls 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 (1) in Conocephalus conicus, and has been recently studied in that species by King (1) and Cavers (1), as well as in several other genera. It is much more marked in the dicecious 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 Marchantia 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 (1) gives the same account of the young archegonium of Preissia commutata. ‘This cer- tainly does not occur in Targionia, and to judge from the later stages of Fimbriaria Californica, this species too lacks this OMe) Yee WYO afte 3 II MUSCINEZZ—HEPATICZ—MARCHANTIALES 71 acteristic lacunar tissue of these forms. In the latter respect Monoclea closely resembles Dumortiera, 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 Marchantiacez, and may perhaps be compared to Targionia. See Ruge (1), Cavers (7), Campbell (19). Résumé 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 Ricciacez 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- siniee and Targioniez, and not a special group opposed to all the other Marchantiacee. 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 lamelle, through Ricciocarpus and Tessalina, where definite air-cham- bers are present, opening by pores of the same form as those of the lower Marchantiez, and separate ventral scales occur—to forms like Marchantia, where the air-chambers are very 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 with 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 Corsinieg, 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 Hepatic belong to the Jungermanniales, which show a greater range of external dif- ferentiation than is met with in the Marchantiacez, but less variety in their tissues, the whole plant usually consisting of almost uniform green parenchyma. In the lowest forms, e.g., Aneura 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 types, 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 Calobryum, 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 Fossombronia we have genera that while still retain; ing the flattened thalloid character, yet show the first formation 72 III 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 Marchantiacez, and in the 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, whose growth is not interrupted by their develop- ment. In the higher leafy forms (Jungermanniacee acro- gynz) 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 differ essentially in their first divisions from those of the Marchantiacee. After the first division in the mother cell, by which the stalk is cut off from the antheridium itself, the first wall in the latter, in all forms inves- tigated except Spherocarpus, 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 Marchantiacee. 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., Pellia 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 Anelaterez, 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 Marchantiacee. 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- marked 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 gemmz are found in many species, and in Blasia special receptacles with multicellular gemmz something like those of Marchantia occur. The Jungermanniales naturally fall into two well-marked series! Anacrogyne and Acrogynz, 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 Haplomitriez show some interesting intermediate forms between the two groups, but all the other Jungermanniales examined belong decidedly to one or the other. Asa rule the Anacrogyne are thallose (the “frondose” forms of the older botanists), but a few genera, especially Fossombronia, show a genuine formation of leaves. All the Acrogynz have a distinct slender stem with large and perfectly developed leaves. 1 Prof. L. M. Underwood proposes the name Metzgeriacez for the Ana- crogyne, reserving the name Jungermanniacee for the Acrogyne. These two groups he considers co-ordinate with the Marchantiales and Antho- cérotes. ut THE JUNGERMANNIALES 75 ANACROGYN Jungermanniales Anacrogyne. Apical cell of female axis never becoming transformed into an archegonium. A. Anelaterez. No true elaters, but sterile cells repre- senting these. Capsule cleistocarpous. Four genera, Thallocarpus, Spherocarpus, Riella, Geothallus. 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—Metzgeriexe, Leptothecez, Codoniez. b. Gametophore upright with three rows of radially ar- ranged leaves. Fam. I., Haplomitriez. ANELATEREE The simplest form belonging here is Spherocarpus, a genus that -shows certain affinities with the Ricciacez, but on the whole seems to be more properly placed at the bottom of the series of the Jungermanniales. Spherocarpus terrestris occurs in Europe and the south- eastern United States. In California it is replaced by two species, S. Californicus and S. cristatus, 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 76 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 Hepatice. The mother cell is much elongated, and the first division wall, by Fic. 30.—Spherocarpus Californicus (?). A, Male plant, X40;