THE STRUCTURE AND DEVELOPMENT OF MOSSES AND FERNS "t^^^y^^ O "* r > C f- The Structure and Development of Mosses and Ferns {Archegon'iatae) 3 THIRD EDITION, REVISED AND ENLARGED BY DOUGLAS HOUGHTON CAMPBELL, Ph.D. Professor of Botany IN THE Leland Stanford Junior University THE MACMILLAN COMPANY London: Macmillan & Co., Ltd. 1928 All rights reserved Copyright, 1905 By the MaCMILLAN COMPANY hec up and electrotyped Published. September, 1905 Reprinted July, 101.I PREFACE TO THE SECOND EDITION Since the first edition of the present work was pub- lished, the number of important investigations on the struc- ture and development of the Archegoniatse has been so great that it has been found necessary to recast entirely certain portions of the work, this being especially the case with the chapters dealing with the eusporangiate Ferns. The whole book, however, has been carefully revised, and a good deal of new matter introduced, including tv/o 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. 7-> ■RE FACE 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 bibHography, 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. vn CONTENTS CHAPTER I Introduction » » c i CHAPTER H MusciNiLE (Bryophyta) — Hepatic^ — Marchantiales 8 CHAPTER HI The Jungermanniales c. .. 72 CHAPTER IV The Anthocerotes « c . . c . . . 120 CHAPTER V The Mosses (Musci) : Sphagnales — Andre^ales 160 CHAPTER VI The Bryales « 18S CHAPTER VII The Pteridophyta — Filicine^ — Ophioglossace^ 229 CHAPTER VIII Marattiales 27^ CHAPTER IX FiLiciNE^ Leptosporangiat^ 305 CHAPTER X The Homosporous Leptosporangiat^ (Filices) 346 CHAPTER XI Leptosporangiat^ Heterospore^ ( Hydro pterides) 396 CHAPTER XII Equisetine^ , 443 CHAPTER XIII LYCOPODINE.E 483 CHAPTER XIV ISOETACE^ c 536 CHAPTER XV The Nature of the Alternation of Generations 562 CHAPTER XVI Fossil Archegoniates 576 CHAPTER XVII Summary and Conclusions 592 ix r-k ^^ CONTENTS Appendix ^7 Bibliography ^45 Index ^^^ CHAPTER I INTRODUCTION Under the name Archegoniatae are included a large number of plants which, while differing a good deal in many structural details, still agree so closely in their essential points of structure and development as to leave no room for doubting their close relationship. Besides the Bryophytes and Pteri- dophytes, which are ordinarily included under this head, the Gymnospermse or Archespermae might very properly be also embraced here, but we shall use the term in its more restricted meaning. The term Archegoniatae 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 Algae there is no form at present known in which the female organ can be certainly compared to the archegonium, although the oogonium of the Characeae recalls it in some respects. The antheridium or male organ of the Archegonlatae, 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 w^ith the, same organ in the Algae, especially the Characeae. Like the archegonium it may be entirely free, or even raised on a long pedicel ; or it may be completely sunk in the tissue of the plant, or even be formed endogenously. It usually consists of a single outer layer of cells containing 2 MOSSES AND FERNS chap. chlorophyll, and these enclose a mass of small colourless cells, the sperm cells, each of which gives rise to a single ciliated spermatozoid. The development of the latter is very uniform throughout the Archegoniatae, and differs mainly from the same process in the higher green Alg?e, especially the Characese, 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 bv 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 &gg. The sexual cells do not differ essentially from those of the higher AlgcT, and point unmistakably to the origin of the Arche- goniatcT from similar aquatic forms. Indeed all of the Archegoniat?e 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 Ancnra, one of the lower Liverworts, but special reproductive buds or gemmae, both unicellular and multicellular, are common in many forms. A very marked characteristic of the whole group is the sharply-marked alternation of sexual and non-sexual stages. The sexual plant or gametophyte varies much in size and complexity. It may be a simple flat thallus comparable in structure to some Alg?e, 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 Marchantiacere, w'hile 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 tgg, 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, c. g., Ophio- glossuni, 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 lo to 15 metres in height, with leaves 5 to 6 metres in length. In the formation of the spores all of the Archegoniatse show great uniformity, and this extends, at least as regards the pollen spores, to the Spermatophytes as well. In all cases the spores arise from cells which at first form a solid tissue arising from the division of a single primary cell, or group of cells (Archesporium). These cells later become more or less I INTRODUCTION 5 completely separated, and each one of these so-called ^'spore mother cells,'' by division into four daughter cells, forms the spores. The young spores are thin walled, but later the wall becomes thicker and shows a division into two parts, one inner layer, which generally shows the cellulose reaction and is called the endospore (intine), and an outer more or less cuticularised coat, the exospore (exine). In addition a third outer coat (perinium, epispore) is very generally present. As the spore ripens there is developed within it reserve food materials in the form of starch, oil, and albuminous matter, and quite frequently chlorophyll is present in large quantity. Some spores retain their vitality but a short time, those of most species of Eqiiisctum 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 tgg 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 ]\Iarattiacere and Equisetace^e, 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 Marattiace?e a year or more sometimes passes before archegonia are formed. These prothallia, too, multiply by budding, much as the Liverworts do. In case no archegonia are fecundated the prothallium may grow until it reaches a length of three or four centimetres, and resembles in a most striking manner a thallose Liverwort. In such large prothallia it is not unusual for more than one archegonium to be fecundated, although usually only one of the embryos comes to maturity, and the prothallium may continue to live for some time after the sporophyte has become independent. Usually, however, as soon as an archegonium is fertilised, the formation of new ones ceases, and as soon as the sporophyte is fairly rooted in the ground the prothallium dies. In most of the lower Pteridophytes the prothallia are monoecious, but in the more specialised ones are markedly dioecious. When this is least marked the males and females differ mainly in size, the latter being decidedly larger; in the more extreme cases the difference is much more pronounced and is correlated with a great reduction in the vegetative part of the gametophyte of both males and females. This reaches its extreme phase in the so-called heterosporous forms. In these the sex of the gametophyte is already indicated by the character of the spore. Two sorts of spores are produced, large and small, which produce respectively females and males. In all of the heterosporic Pteridophytes the reduction of the vege- tative part of the gametophyte is very great, especially in the male plants. Here this may be reduced to a single quite functionless cell, and all the rest of the plant is devoted to tlie formation of the single antheridium. In the female plants the reduction is not so great ; and although sometimes but one archecronium is formed, there mav be in some cases a consider- able number, and owing to the large amount of nutritive material in the spore, in case an archegonium is not fertilised, I INTRODUCTION 7 the prothallium, even if it does not form chlorophyll, may grow for a long time at the expense of the food materials that nor- mally are used by the developing embryo. In strong contrast to the slow growth and late development of the reproductive organs in the homosporous forms, most of the heterosporous Pteridophytes germinate very quickly. The Marsiliacese, in which the female prothallium is extremely reduced, show the opposite extreme. Here the whole time necessary for the germination of the spores and the maturing of the sexual organs may be less than twenty-four hours, and within three or four days more the embryo is completely developed. That heterospory has arisen independently in several widely separated groups of Pteridophytes is plain. The few genera that still exist are readily separable into groups that have comparatively little in common beyond possessing two sorts of spores ; but each of these same forms shows much nearer affinities to certain widely separated homosporous groups. In some of the heterosporous forms the first divisions in the germinating spore take place while it is still within the sporan- gium, and may begin before the spore is nearly fully devel- oped. In other cases the sporangia become detached when ripe, and the spore (or spores), still surrounded by the spo- rangium, falls away from the sporophyte before germination begins. In these respects the heterosporous Pteridophytes show the closest analogy with the similar processes among the lower Spermatophytes, where it has been shown in the most conclusive manner that the ovule with its enclosed embryo-sac is the exact morphological equivalent of the macrosporangium of SelagineUa or AzoUa, for example, and that the seed is simply a further development of the same structure. CHAPTER II MUSCINAE (BRYOPHYTA)— HEPATICAE— MARCHANTIALES The first division of the ArchegoniatcX, the Muscineae or Bryophyta, comprises the three classes, Hepaticae or Liverworts, the Musci or Mosses and the Anthocerotes. In these as a rule the gametophyte is much more developed than the sporophyte, and indeed in many forms the latter is very rarely met with. They are plants of small size, ranging in size from about a milli- metre in length to 30 centimetres or more. A few of them are strictly aquatic, i. e., Riclla and Ricciocarpus among the Hepat- ic3e, 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., Biixbauiuia, the game- tophyte of the Muscineai is abundantly supplied with chloro- 8 CH. II MUSCINEJB— HEPATIC^— 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 Hepaticce, like Aneiira and Pcllia, 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 Algre, 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 Marchantiace^. 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 Hepaticge, but in the foliose Hepaticse and Mosses is with few exceptions a three-sided pyramid. The gametophyte of the Muscineae 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 HepaticcX, but less so in the Mosses, is the formation of gemmae or special reproductive buds. These are produced in various ways, the simplest being the separation of single cells, or small groups of cells, from the margins of the leaves. In the case of Aneura mnltifida they are formed within the cells and discharged in a manner that seems to be identical with that of the zoospores of many Alg?e. Again, multicellu- lar gemmae of peculiar form occur in several of the Hepatic?e, e.g., Blasia, Marchantia, where they occur in special receptacles, ro MOSSES AND FERNS chap. and among the Mosses similar ones are common in Tctraphis and some wiher genera. The archegonia of all the MuscinecX agree closely in their earlier stages, but differ more or less in the different groups at maturity. In all cases the archegonium arises from a single superficial cell, in which three vertical walls are formed that intersect so as to form an axial cell and three peripheral ones. From the axial cell develop the ^gg, canal cells, and cover cells of the neck, and from the peripheral cells the wall of the venter and the outer neck cells. In all IMuscinCcne except the Antho- cerotes the archegonium mother cell projects above the sur- rounding cells, but in the latter the mother cell does not project at all, and the archegonium remains completely sunken in the thallus. In all other forms the archegonium is nearly or quite free, and usually provided with a short pedicel. This is espe- cially marked in the Mosses, where the lower part of the arche- gonium is as a rule much more massive than in the Hepaticae. The most marked difference, however, between the arche- gonium of the Hepaticse and Mosses is in the history of the cover cell or uppermost of the axial row of cells of the young archegonium. This in the former divides at an early period into four nearly equal cells by vertical walls, the resulting cells either remaining undivided, or undergoing one or two more divisions ; but in the Mosses this cell functions as an apical cell, and to its further growth and division nearly the whole growth of the neck is due. The antheridia, except in the Anthocerotes, also arise from single superficial cells, and while they differ much in size and form, are alike in regard to their general structure. The antheridium always consists of two parts; a stalk or pedicel, which varies much in length, and the antheridium proper, made up of a single layer of superficial cells and a central mass of small sperm cells. The former always contain chloroplasts, which often become red or yellow at maturity. The sperm cells have no chlorophyll, but contain abundant protoplasm and a large nucleus, which latter forms the bulk of the body of the spermatozoid found in each sperm cell of the ripe antheridium. The spermatozoids are extremely minute filiform bodies, thicker behind and provided with two fine cilia attached to the forward end. Adhering to the thicker posterior end there may usually be seen a delicate vesicle, which represents the II MUSCINE^— HEPATIC^— MARCH ANTI ALES II remains of the cell contents not used up in the formation of the spermatozoid. When the ripe sexual organs are placed in water their outer cells absorb water rapidly and become strongly distended, while the central cells, i.e., the canal cells of the archegonium, and the sperm cells, whose walls have become mucilaginous, have their walls dissolved. The swelling of the mucilage derived from the walls of the central cells, combined with the pressure of the strongly distended outer cells, finally results in the bursting open of both archegonium and antheridium. In the former, by the forcing out of the remains of the canal cells an open channel is left down to the tgg, 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 ^gg, wdiere it fuses with the egg-nucleus, and thus effects fertilisation. The tgg immediately secretes a cellulose wall about itself, and shortly after the fusion of the nuclei is complete the first segmentation of the young embryo takes place. The origin of the sexual organs is from a single cell, but the position of this cell varies much. In the thallose Hepaticse 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 Hepatic^ and the Mosses, the apical cell of the shoot becomes itself the mother cell of an archegonium, and of course with this the further growth of the axis is stopped. The antheridia in the foliose Hepatic?e are usually placed singly in the axils of more or less modified leaves, but in most Mosses the antheridia form a terminal group. Mixed with the sexual organs are often found sterile hair-like organs, paraphyses, often of very characteristic forms. In the foliose Hepaticse and most Mosses, the archegonia are often surrounded by specially modified leaves, and in the former there is also an inner cup-like perichsetium formed from the tissue surrounding 12 MOSSES AND FERNS chap. the archegonia. In the thallose HepatiCcX, both antheridia and archegonia are generally enclosed by a sort of capsule, similar to the perichaetium of the foliose forms formed by the growth of the tissue of the thallus immediately surrounding them. The Asexual Generation (SporopJiyfc, Sporophorc, Sporogonium) The sporophyte of the ]\Iuscine?e 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 HepatiCcT, 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 SpJiccrocarpus, or more commonly assume the form of elongated cells, — elaters, which assist in scattering the ripe spores. Classification Class I. Hepaticcc {Liverworts) The protonema is either rudimentary or wanting, and usually not sharply differentiated from the gametophore. The gametophore is, with the exception of Haplomitrhim and Calo- hryum, 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 (Aucura mnltifida) or gemmce — (many foliose JungermanniacCcT, 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^— HEPATIC^— MARCH ANTI ALES 13 Class II. Anthocerotcs. Gametophyte, a simple thallus, or sometimes showing a trace of leaf- formation in Dcndroceros; a single large chloro- plast, containing a pyrenoid, in each cell ; archegonium sunk in the thallus, the antheridium endogenous; sporophyte large, with long continued basal growth ; sporogenous tissue derived from the outer tissue (amphithecium) of the embryo. Class III. Miisci (Mosses) The gametophyte shows a sharp separation into protonema and gametophore. The protonema arises primarily from the germinating spore, and may be either a flat thallus or more commonly an extensively branching confervoid growth. Upon this as a bud the gametophore arises. This has always a more or less developed axis about which the leaves are arranged in two, three, or more row^s. 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 gemmae. Both stem and leaves have the tissues more highly differentiated than is the case in the Hepaticce. The archesporium is developed as a rule later than is the case in the Hepaticse, and within is a large central- mass of tissue, the columella, wdiich persists until the capsule is ripe. In most cases there is a large amount of assimilative tissue in the outer part of the capsule, and the epidermis at its base is provided with stomata. The growing embryo breaks through the calyptra at an early stage, and the upper part is in most cases carried up on top of the elongating sporogonium. In very much the greater number of forms the top of the cap- sule comes away as a lid (operculum). THE HEPATIC^ The Hepaticse 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 AMD FERNS chap. Hepaticse with the Mosses one is at once struck with the very much greater diversity of structure shown by the former group, although the number of species is several times greater in the latter. On the one hand, the Hepatic?e approach the Alg?e, the thallus of the simpler forms being but little more compli- cated than that of many of the higher green Algse. On the other hand, tliese 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, c. g., Riccia, is very much like the spore-fruit of Colcochccte, one of the confervoid green Algae; on the other hand, the sporogonium of Anthoccros shows some most significant structural affinities with the lower Pteridophytes. The simplest form of the gametophyte among the Hepaticae is found in the thallose Jungermanniaceae and Anthocerotes. In such forms as Ancura (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 Marchantiaceac, 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- ceae (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 Marchantiaceae also ventral scales or leaf-like lamellae 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 Jungermanniaceae. Between the latter and the strictly thallose forms are a number of interesting inter- mediate forms, like Blasia and Fossomhronia, 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 (Prcissia) thickened sclerenchyma-like fibres occur, n MUSCINE^—HEPA TIC^— MARCH ANTIALES 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- ccphahis) 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., Ivlarchantiace?e, Anthocerotes, a single initial cell is not always to be recognised in the older thallus, Imt in these forms a single initial always appears to be present in the earlier stages. In the Jungermanniacege, how^ever, a single apical cell is always distinguishable, but varies a good deal in form in different genera, at least among the thallose forms, or even in the same genus. Among the foliose Jungermanniacese it always has the form of a three-sided pyramid. From the apical cell seg- ments are cut off in regular succession, and the first divisions of the segments also show much regularity, and often bear a definite relation to the tissues of the older parts. The Sexual Organs The archegonium is always traceable to a single cell, but the position of the mother cell is very different in different genera. In the simplest cases, e.g., Riccia, Splicer ocarpiis (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 growling 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- mcinia (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 Marchantiacese the archegonia are found in the same way, but upon special modi- fied branches. In the foliose Jungermanniacese the origin of the archegonia is somewhat different. Here they are formed upon short branches, where, after a small number of perichaetial leaves have been formed, the subsequent segments of the apical i6 MOSSES AND FERNS chap. cell develop archegonia at once, and finally the apical cell itself becomes the mother cell of the last-formed archegonium, and, of course, with this the growth in length of the branch ceases. With the exception of the Anthocerotes, where the arche- gonium mother cell does not project at all, it quickly assumes a papillate form and is divided by a transverse wall into a basal cell, and an outer one from which the archegonium itself develops. The divisions in this outer cell are remarkably uniform. Three vertical walls are first formed, intersecting so as to enclose a central cell (Fig. 2, G). In this central cell a transverse wall next cuts off a small, upper cell (cover cell) from a lower one. Subsequently the three (or in the Jungermanniaceae 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 {MarcJiantia, species of Ancura), or they are produced in a special part of the ordinary thallus, which usually presents a papillate appearance (e.g., Fiinhriaria). In the foliose Junger- manniace?e 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- tiaceae, Sphccrocarpus) or vertical (Jungermanniace^e). II MUSCINEJE—HEPA TIC^— MARCH ANTI ALES 17 Later, by a series of periclinal walls, a central group of cells is separated from an outer single layer of cells. The latter divide only a few times, and develop chlorophyll, which sometimes changes into a red or yellow pigment at maturity. The inner cells give rise to a very large number of sperm cells, which in most Hepaticse 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 Pcllia especially, where the sperm cells are relatively large, the development has been carefully studied by Guignard ( i ) , Buchtien ( i ) , and others of late years, as well as by many of the earlier observers, and a comparison with other Hepaticae 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 cpiphylla has, according to Guignard ((i), p. 67) from three to four complete coils. Usually when the spermatozoid escapes, it has attached to the coil a small vesicle which swells up more or less by the absorption of water. This vesicle is the remains of the cytoplasm of the cell, and may, perhaps, contain also some of the central part of the nucleus. Gui- gnard ((i), p. 66) asserts that sometimes the cytoplasm is all used up during the growth of the spermatozoid, and that the free spermatozoid shows no trace of a vesicle. In the Ricciaceas and in Sphccrocarpus new archegonia continue to form even after several have been fertilised, so that numerous sporogonia develop upon the same branch of the i8 MOSSES AMD 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 Sphccrocarptis (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 Hepaticas 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 Hepaticce except the lowest ones. The dehiscence of the sporogonium is different in the different orders. In the RicciacCcC and some Marchantiaceae the ripe sporogonium opens irregularly; in a few cases (species of Fimbriaria) the top of the capsule comes off as a lid; ir II MUSCINE^—HEPA TIC^— MARCH ANTI ALES 19 most Jungermanniales the wall of the capsule splits vertically into four valves. The spores are always of the tetrahedral type, i.e., the nucleus of the spore mother cell divides twice before there is any division of the cytoplasm, although this division may be indicated by ridges projecting into the cell cavity, and partially dividing it before any nuclear division takes place. The four nuclei are arranged at equal distances from each other near the periphery of the mother cell, and then between them are formed simultaneously cell w^alls dividing the globular mother cell into four equal cells having a nearly tetrahedral form. These tetrads of spores remain together until nearly full grown, or in a few cases until they are quite ripe. In the ripe spore two, sometimes three, distinct coats can be seen, the inner one (endospore, intine) of unchanged cellulose, the outer one (exospore, exine), strongly cutinized and usually having upon the outside characteristic thickenings, ridges, folds, spines, etc. Where these thickenings are formed from the outside they constitute the third coat (perinium, epispore). The exospore is especially well developed in spe'cies wdiere the spores are exposed to great heat or dryness, and w^hich 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- manniaceae, 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 tlie amount of light is a very important factor in determining the form of the young plant. Thus if the light is deficient, the germ-tube becomes excessively long and slender, and divisions may be entirely suppressed. An excess of light tends to the development at once of a cell surface or cell mass. In the simpler thallose forms the first few divisions in the young plant establish the apical cell, and we cannot properly speak of the gametophore as arising secondarily from a protonema ; in other cases, however, the young plant does arise as an outgrowth or bud from a protonema, which only rarely has the branching filamentous character of the Moss protonema. Classification of the Hepaticae The Hepaticae are readily separated into the two following well-marked orders : Order I Marchantiales. Order II. Jungermanniales. The following diagnoses are taken, with some modifica- tions from Schiffner ((i), p. 5) : Order I. MarcJiaiitialcs. 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 rece])tacles. 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 MUSCINE/B—HEPA TIC^— MARCH ANT I ALES 21 Fam. I. Ricciacccc Chlorophyll-bearing tissue with or without air-chambers, and, where these are present, they never contain a special assim- ilative tissue. Epidermal pores wanting or rudimentary. Sexual organs immersed in open cavities upon the dorsal surface. Sporogonium without foot or stalk, and remaining permanently w^ithin the venter of the archegonium. All the cells of the archesporium produce spores. Fam. 2. CorsiniacecB. 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. MarchafitiacecB Air-chambers usually highly developed, and the chambers often containing a loose filamentous assimilative tissue. Pores upon the dorsal surface always present (except in Diimortiera and Monoclea) and highly developed, ring-shaped or cylin- drical. Sexual organs always in groups, usually upon special long-stalked receptacles. Sporophyte stalked and when ripe breaking through the calyptra, opening by teeth or a circular cleft, more seldom by four or eight valves. The archesporium develops sterile cells, in the form of elaters, as 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 RicciacecX as a group co-ordinate with the Jungermanniales and Marchantiales is not warranted, as more recent investigations, especially those of Leitgeb ( (7), vol. iv.) have shown that the two groups of the Marchantiacese and Ricciacese merge almost insensibly into each other. They are all of them strictly thallose forms, the thallus being unusually thick and fleshy, and range in size from a few millimetres in some of the smaller species of Riccia, to 10 to 20 centimetres in some of the larger species of Dumortiera and Conocephahis. In most of them branching is prevailingly 22 MOSSES AND FERNS CHAP. dichotomous, and as this is rapidly repeated, it often causes the thallus to assume an orbicular outline. Some forms, however, 1 Fig. I. — Marchantiales. A, B, Male plants of Finibriaria Californica, A, from above; B, from below; (^, antheridial receptacle; /, ventral lamellae, X4; C, Riccia glauca, X6; sp, sporogonia; D, Conocephalus conicus, X4; E, Targionia hypophylla, X2; (^, antheridial branch. e.g., Targionia (Fig. i, E), may fork comparatively seldom, and the new branches are for the most part lateral. The thallus II MUSCINE^—HEPA TIC JE— MARCH ANTI ALES 23 is fastened to the substratum by rhizoids, which are unicellular and usually of two kinds, those with smooth walls and those with peculiar papillate thickenings or teeth that project inward (Fig. 12). The cells of the lower layers of tissue are usually nearly or quite destitute of chloroplasts, which, however, occur in large numbers in the so-called chlorophyll-bearing layer, just below^ the dorsal epidermis. This chlorophyll-bearing layer contains air-spaces in all forms except some species of Diimorticra and MonocJca, and these spaces are either simple narrow- canals, as in Riccia glaiica, 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 Marchantiacese. 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 w^hether or not there is a single definite initial cell. Such a single initial is unquestionably present in the earlier stages, and it is quite possible that it may persist, but owing to its small size and its close resemblance to the adjoin- ing cells, this cannot be positively asserted. In vertical sections the initial cell (or cells) appears nearly triangular, with the free outer wall somewhat convex. From this cell two sets of segments are cut off, the dorsal segments giving rise to the green tissue, and the lower segments producing the ventral lamellae and colourless lower layers of cells of the thallus. The plants multiply asexually either by the older parts of the thallus dying away and leaving the growing points isolated, or lateral branches, which are often produced in great numbers from the lower surface of the midrib, become detached and each branch forms a separate plant. The well-known gemmae of Marchantia and Lmmlaria 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 show-s a series of transverse divisions before any longitudinal walls are formed in it. While the gametophyte may reach a very considerable degree of specialisation, the sporophyte is relatively insignifi- 24 MOSSES AND FERNS chap. cant even in the higher forms, and has the foot and stalk poorly developed. While the Marchantiales grow for the most part in moist situations, and some of them, e.g., Marchantia poly- morpha, are very quickly killed by drying, some species, e.g., Riccia frieJioearpa, 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., F'unhriaria Californica, Targionia JiypopJiylla, 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 l^egin, when they absorb water and begin to grow again at once. In these cases usually only the ends of the branches remain alive, so that each growing tip becomes the beginning of a new plant. The Ricciace^ As a type of the simplest of the Marchantiace?e, we may take the genus Riccia, represented, according to Schiffner ((i), p. 14), by 107 species, distrilmted 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 evai)oration of the water they come in contact with the mud at the JDOttom. 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, ,r). 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 lamella? 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 n MUSCINE^—HEPA TIC^—MARCHANTJALES 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, XS25- A, Vertical section through the growing point; x, apical cell; ar, young archegonium; //, ventral lamellae; B-F, successive stages in the development of the archegonium, seen in longitudinal section; G, cross-section of young archegonium (diagrammatic). the thallus is compact, but in the older parts a modification is observable both on the dorsal and ventral surfaces. In the former, a short distance from the growing point, the superficial cells project in a papillate mariner above the surface. This causes little depressions or pits to be formed betw^een the adja- cent cells (Fig. 3, C). The subsequent divisions in the papillre are all transverse, and this transforms each papillate surface cell into a row of cells w^hich, 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 glauco, 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, 1>*« Fig. 3. — Riccia glauca. Horizontal sections of the growing point. A, B, XS25; C, X about 260. C shows the dichotomy of the growing point; x, x', the two new growing points; L, the lobe between them; ar, a young archegonium. they remain in close contact laterally with the neighboring cells, so that instead of forming isolated rows of cells, transverse plates or lamelLx, 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 tw^o rows of ventral scales found in the older parts. Later these scales dry up and n MUSCINE^—HEPA TIC^— MARCH ANTI ALES 27 CT are often scarcely to be detected except close to the growin 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. iiuitans (Leitgeb (7), iv. p. 11) and R. crystallina differ in some respects from the other forms. In these, owing to a greater expansion of the tissues of the older parts of the thallus, the air-spaces are very much enlarged. In the former they are almost completely closed above, as the epidermal cells, by repeated vertical divisions, keep pace with the growth of the thallus and form a continuous epidermis, with only a small central pore over each of the large air-chambers. In R. crys- tallina, however, there is no such secondary growth of the epidermal cells, and in consequence the cavities are completely open above, so that the surface of the thallus presents a series of wide depressions separated by thin lamellae. These two species also show some difference as to the ventral scales. Those of R. Uiiitans are small and do not become separated into two, and in R. crystallina they are wanting entirely. Most of the Ricciaceae multiply by special adventive shoots that arise from the ventral surface of the midrib. These become detached and form new individuals. According to Fellner ( i ) the rhizoids develop at the apex a young plant in a manner entirely similar to that by which the young plant arises from the germ tube of the germinating spore. By far the commonest method of branching in most species of Riccia is a true dichotomy. The first indication of this process is a widening of the growing point and a correspond- 28 MOSSES AND FERNS chap. ing increase in the number of the marginal cells. The central cells of the marginal group now begin to grow more vigorously than the others and to project as a sort of lobe (Fig. 3, C, L), and this lobe divides the initial cells into two groups lying on either side of it. As soon as this is accomplished each new group of initial cells continues to grow in the same manner as the original group, and two new growing points are estab- lished, each of which develops a separate branch. The growth of the middle lobe is limited, and it remains sunk in the fork between the two new branches. The thallus is attached to the substratum by rhizoids of two kinds. The first are smooth-walled elongated cells, with colourless contents, the others much like those of the higher Marchantiacere. 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. glaiica and allied forms four well-marked tissue zones can be readily recognized in such a section. The lowest consists of a few layers of colourless rather loose parenchyma, from which the rhizoids arise, and to which the ventral lamellae are attached. Above this a more compact, but not very clearly limited region," the midrib. The elongated form of the midrib cells, which contain abundant starch but no chlorophyll, is, of course, not evident in cross-section. Radiating from the midrib are closely-set rows of chlorophyll-bearing cells with the charac- teristic narrow air-spaces between. The median furrow is very conspicuous in such a section, and extends for about half the depth of the thallus. Terminating each row of green cells is the enlarged colourless epidermal cells, often extended into a beak-like appendage. In some species, e.g., R. fricJwcarpa, 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 MUSCINEJE—HEPA TICJE— MARCH ANTI ALES 29 continue to form for a long time, so that all stages may be met with upon the same thallus. While both antheridia and arche- gonia may be found together, in the two species R. glauca and R. trichocarpa, mainly studied by myself, I found that as a rule several of one sort or the other would be formed in succession, and that not infrequently antheridia were quite wanting upon plants that had borne numerous archegonia. Both archegonia and antheridia arise from single superficial cells of the younger dorsal segments of the initial cells. In their earliest stages they are much alike, the mother cell of the antheridium being, however, usually somewhat larger than that of the arche- gonium. The cell enlarges and projects as a papilla above the surface, when it is divided by a transverse wall into an outer cell and an inner one. The latter divides but a few times and forms the short stalk ; the outer cell, which has dense granular contents, develops into the archegonium or antheridium as the case may be. In the former case the divisions follow the order already indicated for the typical Liverwort archegonium. In the outer cell, which continues to enlarge rapidly, a nearly vertical wall is formed (Fig. 2, C), which divides the cell into two very unequal parts. This wall is curved and strikes the periphery of the mother cell at about opposite points (Fig. 2, G, i). A second wall of similar form is next formed in the larger cell (G, 2), one end of which intersects the first wall, and finally a third wall (3) intersecting both of the others is formed. The young archegonium seen in vertical section at this stage (Fig. 2, D) shows a large central cell bounded by two smaller lateral ones; in cross-section the central one appears triangular. Each of the four cells of which the arche- gonium rudiment is now composed divides into two. The outer ones each divide by radial walls into equal parts, and the central one divides into an upper smaller cell (cover cell) and a lower larger one (Fig. 3, E).-^ The next divisions are hori- zontal and divide the young archegonium into two tiers of cells. The lower one forms the venter, and the upper one the neck, and next the cover cell divides into four nearly equal cells by intersecting vertical walls. The archegonium at this stage (Fig. 2, F) is somewhat pear-shaped, being smaller at the bottom than at the top, and the basal cell is still undivided. It now rapidly increases in length by the transverse division and growth of all its cells, and there is at the same time a 30 MOSSES AND FERNS CHAP. marked increase in diameter in the venter, which finally becomes almost globular (Fig. 4). The axial cell of the neck, the neck canal cell, divides, according to Janczewski (i), always into four in R. Bischoffii, and the same seems to be true for R. tricJio- carpa (Fig. 4, A), and probably is the same in other species. The number of divisions in the outer neck cells is various, but is most active in the lower part, but in the central cell of the venter there is always but a single transverse division which Fig. 4. — A, Archegonium of Riccia trichocarpa, showing the ventral canal cell (f), XS2s; B, ripe archegonium of R. glauca, longitudinal section, X260. separates the ventral canal cell from the Qgg. 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. BiscJwifii. The basal cell finally divides into a single lower cell whicli remains undivided, completely sunk in the thallus, and an upper cell which divides into a single layer of cells forming part of the venter, and continuous with the other peripheral cells. The mature archegonium (Fig. 4) n MUSCINE^— HEPATIC^— MARCH ANTI ALES 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 ^gg. The cytoplasm is filled with granules, and the nucleus, which is of moderate size, shows a distinct nucleolus, but very little chromatin. A special receptive spot was not certainly to be seen. Almost coincident with the first cell division in the arche- gonium rudiment there is a rapid growth of the cells imme- diately surrounding it. These grow up as a sort of ring or ridge about the archegonium, which is thus gradually immersed in a cup-shaped cavity, and the growth of the cells about this keeps pace with the increase in length of the archegonium, so that even when fully grown only the very extremity of the neck projects above the level of the thallus. The whole process is undoubtedly but a modification of the ordinary growth of the dorsal part of the thallus, and the space about the arche- gonium is the direct equivalent of the ordinary air-spaces. The first division in the primary antheridial cell is the same as in the archegonium, but the later divisions differ much and do not show such absolute uniformity. The first division wall in the upper cell (Fig. 5, B) is always transverse, and this is followed by a second similar wall, but the subsequent divisions show considerable variation even in the same species. After a varying number of transverse walls have been formed, in most cases the next divisions, which are formed only in the middle segments, are vertical, "^and divide the segments into quadrants of a circle when seen in transverse section. Occa- sionally a case is met with where the division walls are inclined alternately right and left, and the divisions strongly recall those of the typical Moss antheridium (Fig. 5, D). The separation of the sperm cells is brought about by a series of periclinal walls in a number of the middle segments, by which four central cells in each segment (Fig. 5, Ti) 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 ® ol Fig. s. — A-F, Development of the antheridium of R. glauca, seen in longitudinal section; G, cross-section of a young antheridium of the same; H, antheridium of R. trichocarpa; I, sperm cells of R. glauca. Figs. E, F, Xiso; I, X6oo, the others X300. part of the wall of the antheridium. The central cells now divide with great rapidity, the division walls being formed nearly at right angles to each other, so that the central part of the antheridium becomes filled with a very large number of nearly cubical cells. The divisions are formed with such regularity that the boundaries of the original central cells remain very clearly marked until the antheridium is nearly mature. The basal cell of the antheridium rudiment in R. glauca divides once by a horizontal wall (Fig. 5, B, D) and forms the short stalk of the antheridium, which, however, is almost completely sunk in the thallus. Between this stalk and the central group of cells there are usually two layers of cells, so that the wall of the antheridium is double at the base, while it has but a single layer of cells in the other parts. The n MUSCINE^—HEPA TIC^— MARCH ANTI ALES 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 Hepaticae, but their excessively small size makes it extremely difficult to follow through the details of their development. When ripe the w^all 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, wdiose 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 ^gg develops at once a cell-membrane and enlarges until it completely fills the cavity of the venter. The first division w^all is more or less inclined to the axis of the archegonium, but approaches usually the horizontal. The lower of the tw^o cells thus formed divides first by a wall at right angles to the first formed, but this is followed in the upper half of the embryo by a similar division, so that the embryo is divided into nearly equal quadrants. In each of the quadrants a wall meeting both of the others at right angles next appears (Fig. 6, C, III), and the embryo at this stage consists of eight nearly equal cells. The next walls are not exactly alike, but the commonest form is a curved w^all (Fig. 6, C) , striking two of the others, usually walls II and III, and intersecting the surface of the embryo. This wall divides the octants into two cells, wdiich 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 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. llieir 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 w^alls the cells separate more and more until they lie free within the cavity of the sporogonium. Each of these spore mother cells is a large globular cell with thin membrane m. Fig. 6. — A, B, Young embryos of R. glaiica in longitudinal section, showing the venter of the archegonium, X260; C, transverse section of a similar embryo, X260; D, longitudinal section of the archegonium and enclosed embryo of R. trichocarpa at a later stage, X220; m, the sterile cells of the sporogonium. and densely granular contents. The nucleus is not so large as is usually the case in cells of similar character, and, except the nucleolus, stains but slightly with the ordinary nuclear stains. In the fresh state these spore mother cells are absolutely opaque, owing to the great amount of granular matter, largely drops of oil, that they contain. In embedding these in paraffine, however, the oil is dissolved and removed, and microtome sections show the fine granules of the cytoplasm arranged in a net-like pattern, the spaces between probably being occupied by oil in the living cells. /I MUSCINE^— HEPATIC^— MARCH ANTI ALES 35 Fig. 7, A shows the nucleus of the mother cell under- going the first division. The small size of the nuclei, and the small amount of chromation in them, make the study of the details of the nuclear division difficult here, and as there was nothing to indicate any special peculiarities these were not followed out. After the first nuclear division the daughter nuclei divide again, after which the four nuclei arrange them- A C. Fig. 7. — Riccia trichocarpa. A, Section ot a spore mother cell undergoing its first division, X600; B, section of young spore tetrad, X300; C, section of ripe spore, X300; D, surface view of the exospore of a similar stage, Xsoo- 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, wdiere 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 Ricciace?e was only known in R. glauca (Fellner (i) ). The account here given is based upon observations made upon R. trichocarpa — a very common Californian species. It fruits in winter and early spring, and the spores remain dormant during the dry summer months. If the spores are sown in the autumn they germinate within a few days by bursting the massive black exospore, through which the colourless endospore enclosing the spore contents projects in the form of a blunt papilla. This rapidly grows out into a long club-shaped filament (Fig. 8, A), much less in diameter than the spore, and into this the spore contents pass. These now contain albuminous granules and great numbers of oil-globules, and some chlorophyll bodies, which at first are small and not very numerous. They, however, increase rapidly in size, and divide also, so that before the first cell division II MUSCINEA^— HEPATIC JE—MARCHANTI ALES 37 takes place the chloroplasts are abundant and conspicuous. The formation of the first rhizoid does not take place usually until a number of divisions have been formed in the young thallus. The first rhizoid (Fig. 9, r) arises at the base of the germinal tube, and is almost free from granular contents. It, usually at least, is separated by a septum from the germ-tube. The first wall in the latter is usually transverse, although in exceptional cases it is oblique (Fig 8, C), and this is followed by a second one parallel to the first (Fig. 8, C). In each of these cells a vertical wall is formed, and then a second at right angles to this, so that the nearly globular mass of cells at the Fig. 8. — Riccia trichocarpa. Germination of the spores, X 190. In E the figure at the left represents a surface view, the one at the right an optical section; K, germinal tube. end of the germ-tube is composed of eight nearly equal cells or octants. As these divisions proceed the oil drops which are so abundant in the undivided germ-tube disappear almost com- pletely, and are doubtless used up by the growing cells. According to Leitgeb's view, and that of other authors, the eight-celled body at the end of the germ-tube is a sort of pro- tonema, from which the gametophore arises as a lateral out- growth. I have seen nothing in the species under consideration which supports such a view. Here the axis of growth is con- tinuous with that of the germ-tube, and in some cases at least, 38 MOSSES AND FERNS CHAP. and probably always, a single apical cell is developed at the apex at a very early stage. Probably this initial ^ell is one of the four terminal octant cells resulting from the first divisions. This cell sometimes has but two sets of segments cut off from it at first, alternately right and left, but whether this form is constant in the young plant I cannot now say. Fig. 9. — Riccia trichocarpa. Later stages of germination. A, from below, X260; B, optical section of A, showing apical cell x, X520; C, X85; r, rhizoids. inter- cellular spaces have begun to develop. The four lower quadrants also divide, at first only by transverse walls, and these cells lengthening give rise to a cylindrical body composed of four rows of cells, terminated by the more actively dividing group of cells at the summit. The single apical cell is soon replaced by the group of initials found in the full-grown gametophyte, and the method of growth from ji MUSCINEAi—HEPA TIC^— MARCH ANTI ALES 39 now on is essentially the same. The growth of the cells in the forward part of the dorsal surface of the young thallus is more active than that of the ventral side, so that they project over the growing point (Fig. 9), and as the outer cells of the lateral segments of the apical cell (or cells) also increase rapidly in size as they recede from the growing point, the forward margin of the thallus, seen from below, is deeply indented, and the forward part of the thallus is thus occupied by a deep cavity, at the bottom of which, toward the ventral side, lies the growing point. This cavity is the beginning of the groove or furrow found in the older thallus. At first the cells of the young thallus are without inter- cellular spaces, but at an early period (Fig. 9, C) the outer cells of the young segments separate and form the beginnings of the characteristic air-spaces. In R. trichocarpa some of the dorsal cells about the same time form short pointed papillae, the first indication of the pointed hairs characteristic of this species. As the plant grows, new rhizoids are formed by the growing out of ventral cells into papillae, which are cut 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 lamellae, which are quite absent from the young plant. Classification of the Ricciace^ Besides the genus Riccia, which includes all but three species of the family, there are two other genera, each represented by a single species, which undoubtedly belong here. Of these Ricciocarpiis nafans is of almost world-wide distribution. It is a floating form, like Riccia Huitans. Leitgeb ( (7), vol. iv.) has made a very careful study of the structure and development of the thallus, 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- chaml>ers 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 Marchantiacese. 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 lx)dies like those found in the Marchantiacese occur. The terrestrial form, which grows on the margins of ponds, etc., where the floating form is found, is much more richly branched and more vigorous than the floating form (Fig. lo). The ventral scales become shorter, and numerous wide but unthick- r^^^ B ened rhizoids are formed, which are almost completely lacking in the floating form. The structure of the reproductive organs and sporogonium are essentially the same as in Riccia. Garber ( i ) , who has recently studied the development of Riccio- carpus, finds that it is not dioecious, as has been frequently asserted. Fig. .o.-Ricciocarpus natans. A, ^ut rather protcraudrous— that is, Floating form; B, terrestrial numcrous authcridia are formed, °^"^' ^^' 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 Ihe 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 numl)er of the plants survive, some- times sinking to the bottom, and resuming growth again in the spring. The third genus, TcsscUna (Oxyniitra), represented by the single species, T. pyrainidata, is much less widely distributed, belonging mainly to Southern Europe, but also found in Para- n MUSCINE^—HEPA TIC JE— MARCH AN TI ALES 41 guay. This interesting form has also been carefully examined by Leitgeb ((7), iv., p. 34), who calls attention to its inter- mediate position between the RicciacCce and the Marchantiacese. 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 dioecious and strictly terrestrial. A third genus, Cronisia, represented also by a single species, C. paradoxa, is placed provisionally with the RicciacCcC by Schiffner ((i), p. 15), but the structure and development have not been investigated with sufficient completeness to make this certain. It has been found only in Brazil. Schiffner says of this form : 'Tt belongs perhaps to the Corsinie?e, and forms a direct transition from the Ricciaceae to that family." The C0RSINIACE.E {Schiffner (i), p. 26), The family Corsiniacese comprises but two genera, Corsinia and Ftmiciilaria (Boschia). Each genus contains but a single known species. Structurally they are intermediate in character between the Ricciace?e and Marchantiacese. Corsinia differs from all the higher Marchantiacese in the character of the ven- tral scales, which are formed in more than two rows, like those of Ricciocarpns. 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 Marchantiacese, but the sterile cells in Corsinia do not develop into true elaters, and in both genera the foot is less developed than in the true Mar- chantiaceae. March ANTiACE^. Comparing the Marchantiaceae with the Ricciaceae, the close similarity in the structure and development of the thallus is at 42 MOSSES AND FERNS chap. once apparent, but the former are more highly developed in all respects. The development of definite air-chambers in the green tissue, and a continuous epidermis with the characteristic pores, is common to all of them with the exception of the peculiar genera Dumorticra and Monoclca, where the develop- ment of the air-chambers is partially or completely suppressed. The genera Ricciocarpus and Tcssaliua on the one hand, and Corsinia and BoscJiia on the other, connect perfectly Riccia with the Marchantiacere as regards the structure of air-spaces and epidermis, as they do in other respects. The epidermal pores in the Marchantiaceae are sometimes simple pores sur- rounded by more or less symmetrically arranged guard cells (Fig. 1 1, D), or they are, especially upon the female receptacles, of a most peculiar cylindrical form, which arises by a series of transverse walls in the primary guard cells (Fig. ii, C). There is a good deal of difference in the character of the air- chambers in different genera. In RchouUa and Fimhriaria, for instance, they reseml:)le a good deal those of Ricciocarpus, a. more or less complete division of the primary chambers being produced by the formation of diaphragms or laminae, which give the green tissue an irregular honey-combed appearance, and in these forms there is not a sharp separation of the green tissue from the ventral colourless tissue. In other genera, Marchantia, Targionia (Fig. ,i8), Conoccphalus, 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 Conoccphalus (Fig. i, D) is especially conspicuous. The bottom of these chambers is sharply defined by the colourless cells that lie below, and the space within the chamber is filled by a mass of short, branching, conferva-like filaments, which in the centre of the chamber have free terminal cells, but toward the sides are attached to the epidermal cells and are more or less confluent with the adjacent filaments. As in Riccia rhizoids of two kinds are present, but the thickenings to the tuberculate rhizoids (Fig. 12) are much more pronounced, and these are not infrequently branched, and may extend nearly across the cavity of the hair. The ventral scales are not produced by the splitting of a single lamella, as in Riccia, but are separate from the first and usually arranged II MUSCINE^—HEPA TIC^— MARCH ANTI ALES 43 in two rows. Leitgeb ((7), iv., p. 17), recognises two types of these organs. In their earhest stages they are ahke, and both arise from papilke close to the growing point. In both cases this papiha is cut off from a basal cell, but in the first type {Smitcria, Targionia, Dnmortiera) 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. rmm> Fig. II. — Fimbriaria Californica. Development of the pores upon the archegonial receptacle, X260. A, B, C, in longitudinal section; D, view from above. size, and forms the overlapping dark purple marginal part of the scale so conspicuous in many species. In different parts of the thallus are found large mucilage cells, which are usually isolated ; or in Conocephahis, according to Goebel's (i) investigations, and those of Cavers (6), they may form rows of cells which become confluent so as to form mucilage ducts. In the earlier stages these cells have walls not differing from those of the adjacent cells, but as they grow older the whole cell wall is dissolved, and the space occupied by the row of young cells becomes an elongated cavity filled with apparently structureless mucilage. These cells are recog- nisable at an early period, as their contents are much denser and more finely granular than those of the adjacent cells. 44 MOSSES AND PERNS CHAP. T 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 Hepaticae, have been carefully studied by Pfeffer (2). The oil body has a round or oval form usually, and in the Mar- chantiCcX 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 Lunidaria, less so in Marchantia and Frt'/^^/a( Cavers (6) ; Kiister ( i ) ). The thallus of the Marchantiace?e is made up al- most entirely of parenchyma, but Goebel (3) states that in Prcissia coinimitata 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 Marchantiaceai have no special non- sexual reproductive organs, but in the genera Fig. 12. — Mar- ,, , ,. . j ,. ., chantia poly- Marcliautia. and Liuiulana special gemmae are pro- nto r p h a . {[^-^qqq[ Jii enormous numbers; and in the latter tubercuiate form, which is extremely common in greenhouses, rhizoid , tiie plant multiplies only by gemmae, as the plants are apparently all female. These gemmae, as is well known, are produced in special receptacles upon the dorsal side of the thallus. The receptacles are cup-shaped in Mar- cJiantia, and crescent-shaped in Lunuhiria, where the forward part of the margin of the cup is absent. These cups are appar- ently specially developed air-chambers, which, closed at first, except for the central pore, finally become completely open. The edge of the fully-developed receptacle is fringed. The gemmae arise from the bottom of the receptacle as papillate hairs, and their development is the same in the other two genera where they occur. Fig. 13 shows their development in M. polymorpha. II M USCINE^—HEPA TIC^—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 A. Fig. 13. — Marchantia polymorpha. A, Plant with gemma cups {k, k), Xz; B-F, development of the gemmae, Xs^s; G, an older gemma, X260; v, v' , the two growing points. equal superimposed cells (Fig. 13, D). The wall III in Fig. 13, D, arises a little later than wall II, and is always more or less decidedly concave upward. Each of the four primary cells of the gemma is divided into two by a central vertical wall, and this is followed by periclinal w^alls 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 gemnicT 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 clul>shaped hairs, which secrete a mucilage that swells up when wet, and finally tears away the gemmae from their single-celled pedicels. The further development of the gemmae depends upon their position as to the light. Whichever side happens to fall down- ward becomes the ventral surface of the young plant, and the colourless cells upon this surface grow out into the first rhi- zoids. The two growing points persist, and the young plant has two branches from the first, growing in exactly opposite directions. As soon as it becomes fastened to the ground the dorsiventrality is established, and upon the dorsal surface the special green lacunar tissue and the epidermis with its charac- teristic pores are soon developed, while the ventral tissue loses its chlorophyll, and soon assumes all the characters found in the mature thallus. The branching of the thallus is in most cases dichotomous, as in Riccia, but occasionally, as in Targionia (Fig. i, F), the growth is largely due to the formation of lateral adventitious branches produced from the ventral surface. In structure and development the sexual organs correspond closely to those of the Ricciaceae, but they are always formed in more or less distinct groups or "inflorescences." As might be expected, this is least marked in the lower forms, especially the Corsinieae (Leitgeb (7), vol. iv.), where the main distinc- tion between them and the lower Ricciaceae is that in Corsinia the formation of sexual organs is confined to a special region, and that the archegonia do not have an individual envelope as in Riccia, but the whole group of archegonia is sunk in a com- mon cavity, which is of exactly the same nature as that in which each archegonium is placed in the latter. In most of the Marchantieae, however, both antheridia and archegonia are lx)rne in special receptacles, which in the case of the latter are for the most part speciallv modified branches or systems of branches, raised at maturity upon long stalks (Fig. 21). The II MUSCINEJE— HEPATIC^— MARCHANTIALES 47 antheridial receptacles are sometimes stalked, but more com- monly are sessile, and often differ but little from those of the higher Ricciacese. The sporogonium shows an advance upon that of the Ricciacese by the development of a lower sterile portion, or foot, in addition to the spore-bearing portion or capsule, and in the latter there are always sterile cells, which in all but the lowest Corsinieas have the form of elaters. At maturity, also, the ripe capsule breaks through the calyptra, except in the Corsiniese, wdiere, too, the sterile cells do not develop into elaters, but seem to serve simply as nourishing cells for the growing spores. The stalk of the capsule is usually short compared with that of most Jungermanniacese, and the wall of the capsule remains intact until the spores are ripe. The spores vary much in size, and in the development of the outer wall. In Marchantia polyinorpha 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 Marchantieae is very much like that of Riccia. In Fimbriarta Calif ornica (Fig. 14) the apical cells seen in vertical section show the same form as those of Riccia, and the succession of dorsal and ventral segments is the same; but here the development of the ventral segments is much greater, and there is not the formation of the median ventral lamellae as in Riccia, but the two rows of ventral scales arise independently on either side of the midrib, very near the growing point, and closely overlap and completely protect the apex. The formation of the lacunae in the dorsal part of the thallus begins earlier than in Riccia, and corresponds very closely to what obtains in Ricciocarpus. The pits are at first very narrow, but widen rapidly as they recede from the apex. In the epidermal cells surrounding the opening of the cavity, there are rapid divisions, so that the opening remains small and forms the simple pore found in this species. As in Riccio- 48 MOSSES AND FERNS CHAP. carpus, the original air-chambers become divided by the devel- opment of partial diaphragms into secondary chambers, which are not, however, arranged in any regular order, and communi- cate more or less with one another. In Targionia (Figs. i8, 19), where the archegonia are borne upon the ordinary shoots, the growth of the dorsal seg- ments is so much greater than that of the ventral ones that the upper part of the thallus projects far beyond the growing point, A. which is pushed under toward the ventral side. A similar condition is found in the archegonial receptacles of other for m s, where this in- cludes the growing point of the shoot (Fig. 21). In Targionia the lacun?e are formed much as in Fiinhriaria, but they are shallower and much wid- er, and the pores corre- spondingly few. The as- similative tissue here re- sembles that of Mar- thantia and others of the higher forms. It is sharply separated from the compact colourless tissue lying below it, and the cells form short con- fervoid filaments more or less branched and an- astomosing, and except in the central part of the chamber united with the epidermal cells. Under the pore, however, the ends are free and enlarged with less chlorophyll than is found in other cells. All of the ]\Iarchantie?e except the aberrant genera Dumor- tiera and Mnnnclca correspond closely to one or the other of the above types in the structure of the thallus, but in the latter the air-chambers are either rudimentary or completely absent, and the ventral scales are also wanting. Leitgeb ( (7), vi., p. 124) Fig. \^.— Fimbriaria Californica. A, Vertical sec- tion through the apex of a sterile shoot, show- ing the formation of the air-chambers ; x, the apical cell, X300; B, similar section through an older part of the thallus. cutting through a pore, X 100. n MUSCINE/E—HEPA TICJE— MARCH ANTIALES 49 investigated D. irrigua, whose thallus is characterised by a pecuhar 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. trichoccphala, 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- tiace?e, and the succession of segments the same, but no indi- cations of lacunae 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 Duinortiera corresponds in its fructification with the higher Marchantie.x, 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. trichoccphala. Sexual Organs The structure and development of the sexual organs are very uniform among the Marchantiaceae. In Fimhriaria Cali- fornica, which is dioecious, the antheridial receptacle forms a thickened oval disc just back of the apex. Not infrequently (Fig. I, A), when the formation of antheridia begins not long before the forking of the thallus, both of the new growing points continue to develop antheridia for a time, and the recep- tacle has two branches in front corresponding to these. The receptacle is covered with conspicuous papilke which mark the cavities in which the antheridia are situated. Vertical longi- tudinal sections through the young receptacle show antheridia in all stages of development, as their formation, like those of Riccia, is strictly acropetal. The first stages are exactly like those of Riccia, and the primary cell divides into two cells, a pedicel and the antheridium proper. The divisions in the lower 4 so MOSSES AND FERNS CHAP. cell are somewhat irregular, but more numerous than in Riccia, so that the stalk of the ripe antheridium is more massive (Fig. 1 6). 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 polyinorpha 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. Bolmidcvi, the antheridia were unusually slender, and fre- quently four, and sometimes five transverse divisions are formed before the first vertical walls appear. Sometimes all the cells divide into equal quadrants by intersecting vertical walls, but quite as often this division does not take place in the uppermost Fig. 15. — Fimbriaria sp. (?). A, Part of a vertical section of a young antheiidial receptacle, showing two very young antheridia ((^), 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 Targioiiia hypophylla, where Leitgeb states that this com- pression is so great that the cells appear like a simple membrane, I found that, so far from this being the case, the cells were extraordinarily large and distinct, and filled the whole space between the body of the antheridium and the wall of the cavity, which in Leitgeb's figures ((7), vi., PI. x., Fig. 12) is repre- II MUSCINE^—HEPA TIC^— MARCH ANTI ALES 51 sented as empty. The antheridium becomes sunk in the thallus precisely as in Riccia. The sperm cells are nearly cubical and the spermatozoid is formed in the usual way. The free spermatozoid (Fig. 16, D) shows 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 Fig. 16.— Fimbriaria Californica. A. Longitudinal section of a fully-developed male receptacle, X8; B, longitudinal section of a nearly ripe antheridium, Xioo; C, young sperm cells, X6oo; D, spermatozoids, X1200. Fimbriaria. In the earlier divisions of the sperm-cells, each cell shows two centrosomes (Fig. 17, i), and Ikeno does not recognise any difference between these and the so-called ''blepharoplast" of Webber and other recent students of sperma- togenesis, who look upon the blepharoplast as a different organ from the centrosome. After the final division, each spermatid is provided with a single centrosome (blepharoplast), from which, later, the cilia arise. 52 MOSSES AND FERNS CHAP, The young spermatid (Fig. 17, 3) is triangular in section, and the blepharoplast is situated in the acute angle which later forms the anterior end of the spermatozoid. The blepharoplast becomes somewhat elongated, and from it grow out the two cilia before any marked change is observable in the nucleus. (Fig. 17, 5). Before the cilia can be seen, there appears in the cytoplasm a round body which stains strongly, but whose origin is not clear. This body Ikeno calls the chromatoid ''Neben- korper," and says that it does not participate directly in the development of the spermatozoid, but ultimately disappears. His figures 30 and 31, however, look as if the portion of the spermatozoid between the blepharoplast and the nucleus was derived from this "nebenkorper," and not from the cytoplasm, as he states is the case. Fig. 17. — Marchantia poly)norfha. Development of the spermatozoid, i. Sperm-cells from the young antheridium; 2, final division of the sperm-cell to form the two spermatids; 2-7, 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 II MUSCINEJE— HEPATIC JE— MARCH ANTI ALES S3 specialised forms are found in the genus Marchantia 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 Anthoccros, 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., M. geminata, the branches of the receptacle are extended and its compound character is evident. The discharge of the spermatozoids from the ripe anther- idium may take place with great force. In the case of Fimbriaria Calif ornica, Peirce (i) found they were thrown vertically for more than fourteen centimetres. The mechanism involved includes not only the tissues of the antheridium itself, but also the cells below the antheridium, and those forming the 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 (i) in Conoccphaliis coniais, and has been recently studied in that species by King (i) and Cavers ( i), as well as in several other genera. It is much more marked in the dioecious species. The archegonia are never sunk in separate cavities, but stand free above the surface of the thallus. The simplest form may be represented by Targionia. Here the archegonia arise in acropetal succession from the dorsal segments of the initial cells of the ordinary branches. A superficial cell enlarges and is divided as in Riccia into an outer and an inner cell. The latter undergoes irregular divisions and its limits are soon lost. In the outer cell the divisions occur in the same order as in Riccia, but from the first the base of the archegonium is broad and not tapering. Strasburger (2) states that in 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 ( i ) 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 Fiinhriaria Calif ornica, this species too lacks this B Fig. i8. — Targionia hypophylla. A, Longitudinal section of the thallus, Xioo; ar, archegonia; / /. ventral scales; B, median section through a pore, showing the assimilating cells (c/) below, X300. division. The full-grown archegonium is of more nearly uniform thickness than in Riccia, as the venter does not become so much enlarged. The neck canal cells are more numerous, about eight being the common number, but in Targionia the formation of division walls between these is sometimes sup- II MUSCINE^—HEPA TIC^— MARCH ANTI ALES 55 pressed (Fig. 19, C), so that this may account for Janczewski's error in stating that the number was always four, as the nuclei in unstained sections might very easily be averlooked. The cover cells are somewhat smaller than in Riccia and do not usually undergo as many divisions, there being seldom more than six in all. In Targionia (Fig. 23, A), and Strasburger ((21), p. 418) observed the same in Marchantia, the ripe ^gg shows a distinct "receptive spot," that is, the upper part of the unfertilised Qgg is comparatively free from granular cytoplasm, while the lower part, about two-thirds in Targionia, is much more densely granular. The nucleus is not very large and has very little chromatin. The nucleolus is large and distinct and / A, D Fig. 19. — Targionia hypophylla. A, Longitudinal section of the apex of the thallus, with young archegonia {ar), X525; x, the apical cell; B, young, C, older arche- gonium in longitudinal section; D, cross-section of the archegonium neck, X52S. Stains very intensely. As the archegonium of Targionia matures, its neck elongates rapidly and bends forward and upward, no doubt an adaptation to facilitate the entrance of the spermatozoid. A similar curving of the archegonium neck is observed in other forms where the archegonium is upon the lower side of the receptacle. After an archegonium (or sometimes several of nearly equal age) is fertilised, the growth in length of the thallus stops. 56 MOSSES AND FERNS THAP. but there is a rapid lateral growth with results in the formation of two valves, which meet in front much like the two parts of a bivalve shall, and this involucre completely encloses the devel- oping sporogonium. In the simplest cases, where the archegonia are borne upon a receptacle^ whicli is raised upon a stalk, e.g., Phgiochasma, Clcvca (Fig. 20, A), the receptacle does not represent, accord- ing to Leitgeb ( (7), vi., p. 29), a complete branch, but is only a dorsal outgrowth of the latter, which may grow out beyond' it, or even form several receptacles in succession. Tlie first indi- cation of tlie recep- A. B. tacle is a dorsal prom- inence whicli soon be- comes almost hemi- spherical, and near the _ .— v: hinder margin the first archegonium arises, without, apparently, any special relation to the growing point. On the lateral margins are then formed two other archegonia, not, however, simultane- ously; and finally a fourth may be formed in front : three or four archegonia in all seem to be the ordinary Fig. 20.-A. Chvea sp. A, longkudinal section of 'l^^nil^er. TllC Stalk of the thallus showing the dorsal origin of the fc- tllC rCCCptaclc is alsO male receptacle ($) ; r, the growing point (dia- .1^,-,,^1 nnnpnrHo-p ni gram after Lcitgcb) ; B, Reboulia hemisphwrica ^ < 'Ol ^ai appCnCiage OI (Radd.), longitudinal section of very young re- tllC tlialluS, aud UOt 1 ceptacle with the first archegonium (Q) ; x, the i • - .• .• apical cell. X300 (after Leitgeb). ^ d 1 r C C t COntinUatlOU of it. The next type is that whicli Leitgeb attributes to GriiuaJdia, Reboulia, Fimbriaria, and some others, but it is not tlie tvpe found in Fimbriaria Calif ornica. In this type tlie structure of "The sporongotiial receptacle of the Alarchantierc is sometimes known as the Carpocephalnm. MUSCINEJE— HEPATIC^— MARCH ANTI ALES 57 the receptacle and the origin of the archegonia are the same :is in that just described; but here the growing point of the A. B D Fig. 2i.—Fimhriaria Californica. A, Plant with two fully-grown sporogonial recep- tacles, natural size; B, single receptacle, X4; C, the same cut longitudinally, showing the sporogonium {sp), enclosed in the perianth {per); D, nearly median section of a young receptacle, showing one growing point (..r) and an arche- gonium (or); L, air-spaces; st, a pore; r, rhizoids, X40; E, the growing point of the same with an archegonium, X300; x, the apical cell. Dranch forms the forward margin of the receptacle, and the stalk is a direct continuation of the axis of the branch, Upon 58 MOSSES AND FERNS chap. its ventral surface it shows a furrow in which rhizoids are produced in great numbers, and this furrow^ continues along the ventral surface of the thallus. The highest type is that of Leitgeb's "Composit?e." In this form the female receptacle is a branch system similar to that of the male receptacle of Marchantia. The branching is usually completed at a very early period, while the receptacle is almost concealed in the furrow in the front of the thallus. A simple case of this kind is seen in Fimbriaria Calif ornica (Fig. 21). In this case there are four growing points that have arisen from the repeated dichotomy of the primary growing point of the branch, and each of these gives rise to archegonia in acropetal succession, much as in Targionia, but the number of archegonia is small, not more than two or three being as a rule formed from each apex. The development of the dorsal tissue is excessive and the ventral growth reduced to almost nothing, and the growing apices are forced under and upward and lie close to the stalk, and the archegonia have the appearance of being formed on the ventral side of the shoot, although morphologic- ally they are dorsal structures. In the common Marchantia polymorpha the branched character of the receptacle is empha- sised by the development of the "middle lobe" between the branches. These lobes grow out into long cylindrical appendages between the groups of archegonia, and give the receptacle a stellate form. Usually in M. polymorpha there are eight growing points in the receptacle, and of course as many groups of archegonia, which are more numerous than in any other genus, amounting to a hundred or more in one recep- tacle. In Marchantia, as well as some other genera with com- pound receptacles, there are tw^o furrows in the stalk, showing that the latter is influenced by the first dichotomy. While the archegonia, before fertilisation, are quite free, the whole group of archegonia, and indeed the Avhole receptacle, is invested with hairs or scales of various forms that originate either from the epidermis of the dorsal side, or as modifications of the ventral scales. The peculiar American genus Cryptoniitriuiu has been investigated by Abrams ( i ) and Howe (3), who finds the devel- opment of the carpocephalum to agree essentially with that of Fimbriaria Californica. Cavers (6, 7, 8), has recently investi- gated that of Conoccphalus {Fcgatclla) , Rcboiilia and Prcissia. n MUSCINE^— HEPATIC^— MARCH ANTI ALES 59 The lacunar tissue is very much developed upon the receptacles, as are to an especial degree the peculiar cylindrical breathing pores. The formation of these begins in the same way as the simple ones, being merely the original opening to the air-space. This seen from the surface shows an opening with usually five or six cells surrounding it. Vertical sections show that very soon the cells surrounding the pore become deeper than their neighbours and project both above and below them. In these cells next arise (Fig. 11, A, B) a series of inclined walls by which each of the original cells is transformed into a row of several cells, and these rows together form a curious barrel-shaped body surrounding the pore. The upper cells converge and almost close the space above, and this is still further diminished by the cuticle of the outer cell wall of the uppermost cells growing beyond the cells and leaving simply a very small central opening. The rows of cells also converge below, and in Fimhriaria Calif ornica the lowermost cells are very much enlarged, and probably serve to close the cavity completely at times, and act very much like the guard cells of the stomata of vascular plants. In Leitgeb's group of the Astroporae, the simple pores of the thallus have the radial walls of the surrounding cells strongly thickened, so that the pores seen from the surface appear star-shaped. The most special- ised of the Marchantieae, /. c, Marchantia, Prcissia, etc., have the cylindrical pores upon the vegetative part of the thallus as well as upon the receptacle, but in the others they occur only upon the latter. The Sporophyte. The first divisions in the embryo of the Marchantiacese and Corsiniacea^ are the same as in the Ricciaceae, but only the upper part (capsule) of the sporogonium develops spores, while the rest becomes the stalk and foot. The simplest form of capsule is found in the genera Corsinia and Boschia, which have been carefully studied by Leitgeb ((7), iv., pp. 45-47). In these the embryo, instead of remaining globular as it does in Riccia, elongates and very early becomes differentiated into a nearly globular upper part, or capsule, and a usually narrower basal portion, the foot (Fig. 22). In the capsule at a very early period a single distinct layer of outer cells is separated from the central group of cells, and forms the wall of the 6o MOSSES AND FERNS chap. capsule, which in Bosch ia at maturity develops upon the inner cell walls thickened bars. Only a portion of the cells of the central part produce spores ; the remainder do not divide after the spore mother cells are formed, but remain either as simple slightly elongated nourishing cells (Corsiiiia) or elaters (Boschia). The other Alarchantiacene are much alike, and as Targioiiia was found to be an especially satisfactory form for study, on account of the readiness with which straight sections of the embryo could be made, it was taken as a type of the higher Marchantiales. The first division wall (basal wall) is trans- verse, and divides the embryo into two nearly equal parts. This is followed in both halves by nearly vertical walls (quadrant walls), and these and the basal wall are then bisected by the octant walls, so that as in Riccia the young embryo is formed of eight nearly equal cells. In Targionia, even at this period, the embryo is always somewhat elongated instead of globular. The next division walls vary a good deal in different individuals. Fig. 23, C shows a very regular arrangement of cells, where the first divisions were much the same in all the quadrants. Here all the secondary walls were nearly parallel with the basal wall, and intersected the quadrant and octant walls; but quite as often, especially in the upper half of the embryo, these secondary walls may intersect the basal wall. In no cases seen was there any indication of a two-sided apical cell such as Hofmeister figures for Tar- FiG. 22. — Corsinia march an- . . . 111 1 • tioicics. voun« sporogo- gjoiiia, aud probably his error arose nium. optical section. X300 from a studv of foHTis Avhcrc the quad- (Leitgeb). „ ' ,.,.,. rant walls were somewhat mclmed, m which case the intersection of one of the secondarv walls with it might cause the apex of the embryo to be occupied by a cell that, in section, would appear like the two-sided apical cell of the Moss embryo. The regular formation of octants was ob- served by me in Fimbriaria Calif ornica, and by Kienitz-Gerloff MUSCINE^— HEPATIC^— MARCH ANTI ALES 6i (i, 2) and others in Mar chant ia, Gr'wialdia, and Preissia, and probably occurs normally in all Marchantiacese. After the tirst anticlinal walls are formed in the octants, no Fig. 23.—Targiorna hypofhylla. A, Longitudinal section of the venter of a ripe archegonium, X500; B-E, development of the embryo, seen in longitudinal median section— B, two-celled, D, four-celled stages, X500 except E, which is magnified 150 times; F, median section of the upper part of an older embryo, X250. definite order could be observed in the succeeding cell divisions, especially in the lower half of the embryo. In the upper part 62 MOSSES AND FERNS ;hap. pericllnal walls appear, but not at any stated time, so far as could be made out, and the first ones do not, as Leitgeb asserts, necessarily determine the separation of the archesporium, as in the Corsinieae. The growth now becomes unequal, the cells in the central zone not dividing so actively, a marked constriction is formed, and the young sporogonium becomes duml>bell shaped. By this time a pretty definite layer of cells (Fig. 2^, F) is evident upon the outside of the capsule, but the cells of the globular lower part, or foot, are nearly or quite uniform. They are larger than those of the capsule, and more transparent. Fig. 24. — Targionia hypophylla. A, Median longitudinal section of older embryo enclosed in the calyptra (cal), X8o; B, a portion of the upper part of the same embryo, X480; the nucleated cells represent the archesporium; C, part of the archesporium of a still later stage; el, elaters; sp, sporogenous cells, X480. In the latter the wall becomes later more definite, and remains but one cell thick until maturity. The arrangement of the cells of the archesporium is very irregular, and until the full number of these is formed they are all much alike. Just before they separate, however, careful observation shows that two well- marked sorts of cells are present, but intermingled in a perfectly irregular way A part of these cells are nearly isodiametric, the others slightly elongated, and the nuclei of the former cells II MUSCINE^—HEPA TIC^— MARCH ANTI ALLS 63 are larger and more definite than those of the latter. At this stage the cells hegin to separate by a partial deliquescence of their cell walls, and when stained with Bismarck-brown these mucilaginous walls colour very deeply, and the cells are very distinct in sections so treated. They finally separate com- pletely, and the much-enlarged globular capsule now contains a mass of isolated cells of two kinds, globular sporogenous cells and elongated elaters. The former now divide into four spores, but before the nucleus divides the division of the spores is indicated by ridges which project inward and divide the cavity of the mother cell much as in the Jungermanniacese. With the first divisions in the embryo the venter of the Fig. 25. — Fimhriaria Californica. A, Young, B, older embryo in median section. A, X300; B, Xioo; C, upper part of a sporogonium, after the differentiation of the archesporium, X 200. archegonium. which before was only one cell thick, divides by a series of periclinal walls into two layers of cells, which later undergo further divisions, so that the calyptra surrounding the older capsule may consist of four or more layers of cells. The neck of the archegonium remains unchanged, but the tissue of the thallus below the archegonium grows actively, and sur- rounds the globular foot, which has grown down into the thallus for some distance, and only the capsule remains within the calyptra. This large growth of the foot is at the expense of the surrounding cells of the thallus, which are destroyed by its 64 MOSSES AND FERNS CHAP. growth, and through the foot nourishment is conveyed from the thallus to the developing capsule. That is, the sporogo- nium is here a strictly parasitic organism, growing entirely at the expense of the thallus. The further growth of the spores and elaters was studied in Finihriaria Calif ornica. The spores remain together in tetrads, until nearlv ripe. In sections parallel to the surface of the younger spores (Fig. 26, C) the outer surface of the exospore is covered with very irregular sinuous thickenings, at first projecting but little above the surface, but afterward becoming in this species extraordinarily developed. In sections of the Fig. 26. — Fimbriaria Californica. A, Young elater X6oo; B, a fully-grown clater, X300; C, surface view of the wall of a young spore, showing the developing episporic ridges, X6oo; D, section of a wall of a ripe spore, X300. ripe spore (Fig. 26, D) three distinct layers are evident, the cellulose endospore, the thick exospore, and this outer thick- ened mass of projecting ridges which has every appearance of being deposited from without, and must therefore be charac- terised as epispore (perinium) ; Leitgeb ((7), vi., p. 45) dis- tinctly states that thickenings of this character do not occur in the MarchantiecT, but that the thickenings are always of the character of those in Riccia. II MUSCINE^— HEP ATICM— MARCH ANTI ALES 65 The elaters are at first elongated thin-walled cells with a distinct although small nucleus, and nearly uniformly granular cytoplasm. As they grow the cytoplasm loses this uniform appearance, and a careful examination, especially of sections, shows that the granular part of the cytoplasm begins to form a spiral band, recalling somewhat the chlorophyll band of Spirogyra. This is the beginning of the characteristic spiral thickening of the cell wall, and while at first irregular, the arrangement of the granular matter becomes more definite, and following the line of this spiral band of granules in the cyto- plasm, there is formed upon the inner surface of the wall the regular spiral band of the complete elater. This band, which is nearly colourless at first, becomes yellow in the mature elater, and in Targionia, where there are generally two, they are almost black. Not infrequently branched elaters are found, but these are unicellular, and no doubt owe their peculiar form to their position between the spore mother cells in the young archesporium. An axial row of granules, which seem to be of albuminous nature, remains in the elaters of Fimhriaria until maturity. The differences in the structure of the sporogonium in dift'erent genera of the Marchantiere are slight. In Marchantia polymorplia, the young sporogonium is nearly globular, and even when full grown it is ellipsoid with the stalk and foot quite rudimentary. Most forms, however, have the foot large, but the stalk, compared with that of most Jungermanniacere, is short. • In most of them the whole of the upper half of the young embryo develops into the capsule, but in Fimhriaria Calif ornica I found that the archesporium was smaller than in other forms described, and that sometimes the apical part of the sporogonium Avas occupied by a sort of cap of sterile cells (Fig. 25, C). When ripe, the cells of the capsule-wall in Targionia de- velop upon their walls dark-colored annular and spiral thicken- ings much like those of the elaters. These thickenings are quite wanting in Fimhriaria. The dehiscence of the capsule is either irregular, e.g.. Targionia, or by a sort of lid, e.g., Grimaldia, or by a number of teeth or lobes, e.g., Liimilaria, Marchantia. In some forms after fertilisation there grows up about the archegonium a cup- shaped envelope, "perianth, pseudoperianth," which in Fim- 5 6S MOSSES AND FERNS CHAP. hriaria especially is very much developed, and projects far beyond the ripe capsule (Fig. 21). The germination of the spores corresponds in the main with that of Riccia. Except in cases where the exospore is very thin, in which case it is not ruptured regularly, the exospore either splits along the line of the three converging ridges upon A^ Fig. 27. — Targionja hypophylla. Germination of the spores, X about 200. In B two germ tubes have been formed; C and E are optical sections; x, apical cell; r, primary rhizoid; sp, spore membrane. the ventral surface, and through this split the endospore pro- trudes in the form of a papilla, as in Riccia; or in Targionia (Fig. 2^) the exospore is usually ruptured in two places on opposite sides of the spore, and through each of these a filament protrudes, one thicker and containing chlorophyll, the other more slender and nearly colourless. The first is the germ tube, the second the first rhizoid. In Finihriaria Californica the first rhizoid usually does not form until a later period. In Targionia a curious modification of the ordinary process is quite often met with (Fig. 27, B). Here, by a vertical divi- sion in the very young germ tube, it is divided into two similar cells, which both grow out into germ tubes. Whether both of these ever produce perfect plants was not determined, but the first divisions in both were perfectly normal. The first divisions in the germ tube are not quite so uniform as in II MUSCINE^—HEPA TIC^— MARCH ANTI ALES 67 Riccia trichocarpa, but resemble tbem very closely in the com- moner forms. In Fimbriaria especially, and this has also been observed in Marchantia (Leitgeb (7), vi., PI. ix., Fig. 13) and other gen- era, a distinct two-sided apical cell is usually developed at an early period, and for a time the growth of the young plant is due to the segmentation of this single cell. Finally this is replaced by a single four-sided cell (Fig. 29, C), very much like the initial cell of the mature thallus. The young plant, composed at first of homogeneous chlorophyll-bearing cells, grows rapidly and develops the characteristic tissues of the older thallus. The first rhizoids are always of the simple form, and the papillate ones only arise later, as do the ventral scales. Tar- gionia shows a number of pe- culiarities, being much less uniform in its development than Fimbriaria. While it often forms the characteristic germ tube, and the divisions there are the same as in Riccia and Fimhriaria, the formation of a germ tube may be com- pletely suppressed, and the Fig. zS.—Targionia hypophylla. Germ f^j-g^ rCSUlt of gCrminatioU is plant in which the thallus (T) has . ., /• i • t. been formed secondarily, X260. oftCU a CCll maSS, from whlCh later a secondary germ tube may be formed with the young plant at the apex (Fig. 28). Such cases as these are the only ones where it seems really proper to speak of the plant arising secondarily from a proto- nema, for in other cases, as in Riccia, the growth is perfectly continuous, and the axis of the young thallus is coincident with that of the germ tube, and^n no cases observed by me could it in any sense be looked upon as a secondary lateral growth. Biology of the Marchantiaceae While the Marchantiaceae are, as a rule, moisture-loving plants, still some of them are markedly xerophilous. Most of the commoner Californian species, e.g., Fimhriaria Californica, Targionia hypophylla, Cryptomitrium teneritm, dry up com- Fig. 2g.—Fimbriaria Californica. A, B, Young plants in optical section, showing the single two-sided apical cell (.r;, X260; C, horizontal section of an older plant with a single four-sided initial (jr), X425; D, E, two young plants, D from below, E from the side, X8s. n MUSCINE^—HEPA TIC^— MARCH ANTI ALES 69 pletely during the long rainless summer, and revive imme- diately with the advent of the autumn rains. In these species, the growing point of the thallus, with a good deal of the adjacent tissue, survives, and at once becomes fresh and active. The scales and mucilage-cells found about the apex are doubt- less water conservers, and according to Cavers (3, 6, 7), the tuberculate rhizoids are also concerned in holding water. In Finihriaria Calif or nica, even the young antheridia survive the long summer drought. It has been shown (Cavers (6, 7)), that the large hyaline cells terminating the green assimilating filaments in the air- chambers of such forms as Conocephalus and Targionia are the principal agents in the transpiration of water from the under- lying tissues. Besides the formation of definite gemmae like those of Marchantia and Liinnlaria, the thallus in most Marchantiacese is capable of extensive regeneration, even from small frag- ments. In Conocephalus there have also been found tuberous outgrowths, which are formed under certain conditions and are doubtless for propagation (Cavers (6)). The Marchantiaceae are readily separable into two sub- families, the Targionieae, and the Marchantiese. Leitgeb has made a further division of the latter family, but some of the characters given are not sufficiently constant to warrant his division, and for that reason it has been thought best not to accept them. Thus Fimhriaria Californica, wdiich is, in regard to its fructification, typical, has the female receptacle of the composite type, a character which, according to Leitgeb. not only does not belong to the genus Fimhriaria, but is not found in any genus of the group (Operculatae) to which he assigns it. This species too does not have the capsule opercu- late, but opens irregularly. The Targionieae include the two genera Targionia, which has been already described at length, and Cyatlwdiuin (Leitgeb (7), vi., p. 136), whose development is not sufficiently known to make its systematic position quite certain. In the position of the sexual organs, and the formation of the two-valved involucre about the fruit, as well as the position of the latter, it corresponds closely to Targionia, but the structure of the thallus is extraordinarily simple, there being practically but two layers of cells with large irregular air-chambers between. While two TO MOSSES AND FERNS chap. sorts of rhizoids are present, those that represent the papillate type of the other IMarchantiacese, while thicker walled than the others, do not dev^elop the projecting prominences. Indeed the whole structure of the plant is curiously reduced, and Leitgeb describes it as resembling the young plants of Mar- chantia or Prcissia. The development of the sexual organs is but imperfectly known, and the suggestion of Leitgeb's that possibly the antheridium is reduced to a single cell, seems hardly probable in view of the structure of the rest of the plant. The sporogonium has the stalk and foot exceedingly rudimentary, but the upper part of the capsule shows a zone of cells whose walls are marked by peculiar ring-shaped thickenings, and opens regularly by a number of teeth, which on account of the thick- ened bars upon the cell wall offer a superficial resemblance to the peristome of the Bryales. As in Targionia the archegonia arise near the apex of the ordinary shoots, and no proper receptacle is formed. All of the other forms have the archegonia borne upon a special receptacle, which, as the sporogonia develop, is raised upon a stalk. Here belong, according to Schiffner ( i ) sixteen genera with about 150 species. The receptacle may be, as we have seen, strictly dorsal in origin, or it may include the grow- ing point of the archegonial branch, or finally it may be a branch system arising from the repeated dichotomy of the original growing point. MONOCLEA The genus Monoclca includes two known species, M. Forsteri, found in New Zealand and Patagonia, and M. Gottschei, of Tropical America, said also to occur in Japan. This genus has been usually associated with Jungermanniales (Leitgeb (7), vol. iii., Schiffner (i)), but a more complete study of the plant has shown that its affinities are undoubtedly more with the simpler Marchantiacese. The structure and posi- tion of the sexual organs, especially the antheridia, and the development of the sporophyte, so far as it has been made out (Cavers (7), Johnson (3)), all point unmistakably to a rela- tionship with the Alarchantiaceae. Two kinds of rhizoids are present, although not so marked as in the typical Marchantiaceae, but the thallus lacks the char- II MUSCINEJE—HEPA TIC^— MARC HAN TI ALES 71 acteristic lacunar tissue of these forms. In the latter respect Monoclca closely resembles Dtiinorticra, and as in that genus, the absence of the air-chambers may be attributed to the semi- aquatic habit of the plant. Monoclca evidently belongs to the lower series of Marchantiaceae, and may perhaps be compared to Targionia. See Ruge (i), Cavers (7), Campbell (19). Resume of the Mar chant ialcs 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 dift'erence of opinion as to where certain genera belong. That the Ricciaceae cannot be looked upon as a distinct order is plain, and they may perhaps be best regarded as simply a family co-ordinate with the Cor- siniese and Targioniege, and not a special group opposed to all the other Marchantiaceae. The gradual increase in complexity of structure is evident in all directions. First the thallus passes by all gradations from Riccia — with its poorly defined air- chambers with no true pores and single ventral lamellae, through Ricciocarpns and Tcssalina, where definite air-cham- bers are present, opening by pores of the same form as those of the lower Marchantieae, and separate ventral scales occur — to forms like Marchantia, where the air-chambers are 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 Tcssalina, with a similar absence of a stalk, but the first indication of sterile cells, through the Coi'siniccc, 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 Finihriaria. CHAPTER III THE JUNGERMANNIALES A VERY large majority of the Hepatic?e belong to the Jungernianniales, which show a greater range of external dif- ferentiation than is met with in the Marchantiacere, Ixit less variety in tlieir tissues, the whole plant usually consisting of almost uniform green parenchyma. In the lowest forms, e.g., Aneiira and Mctzgeria, 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- mitriuiu, and Calohrynni, 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 73 Ill THE JUNGERMANNIALES 72 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 Marchantiace?e, 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 directlv concerned in their formation. The archesfonia 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 (Jungermanniacese acro- gynse) they occur in groups at the end of special branches, whose apical cell finally itself becomes the mother cell of an archegonium, and with this the growth in length of the branch ceases. The antheridia in most cases dififer essentially in their first divisions from those of the Marchantiaceae. After the first division in the mother cell, by wdiich the stalk is cut off from the antheridium itself, the first wall in the latter, in all forms inves- tigated except Sphccrocarpiis, Riella and Geothalhis, 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 ahvays biciliate. The embryo differs in its earliest divisions from that of the Marchantiacese. 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 {c. g., PelUa and most anacrogynous forms), or it may be transverse. From the upper of the tT\'o 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 wall be taken up when considering these. All of the Jungermanniales, except the Anelaterese, 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 Marchantiace?e. 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 wnth 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 JMosses, and sometimes long-lived and produc- ing numerous gametophores. Non-sexual reproductive bodies in the form of unicellular gemnicX are found in many species, and in Blasia special receptacles with multicellular gemmae something like those of AlarcJianfia occur. The Jungermanniales naturally fall into two well-marked series,^ Anacrogyuce and Acrogynae, based upon the position of the archegonia. These in the former are never produced directly from the apical cell of a branch, in the latter group the apical cell of the archegonial branch always sooner or later becomes transformed into an archegonium. The Haplomitrie?e show some interesting intermediate forms between the two groups, but all the other Jungermanniales examined belong decidedly to one or the other. As a rule the Anacrogynae are thallose (the "frondose" forms of the older botanists), but a few genera, especially Fossouibrouia, show a genuine fonnation of leaves. All the Acrogynae have a distinct slender stem with large and perfectly developed leaves. ' Prof. L. M. Underwood proposes the name ^Metzgeriacere for the Ana- crogynre, reserving the name Jungermanniace