fertilization of an archegonium, it is evident that an enormous number of them must perish. The archegonia also proceed from one cell, through the division of which their construction is accomplished. They always take their origin from the cells of the upper surface, and the same is the case with those of Anthoceros, which, however, are sunk into the tissue of the thallus, so that their neck and ventral portions remain united with the tissue of the thallus and do not project freely over it. The distribution of the organs of sex is either monoecious or A B hu hu B A 10. 4.-A. A leafy (follose) Jungermannia (Chiloscyphus polyanthos corda) with three sporogonia; on the right above is one with the capsule open, while in the two others it is still closed. B. A "perianthium," with the perichatial leaves below. are formed; they may frequently be seen to spring from the margin and the mid-rib of the thallus of Metzgeria furcata. The ramification of the foliose Liverworts is a very complex one, but is never of a really forked character. The branchlets commonly stand below the leaves on the sides of the stem. The above-mentioned "adventitious shoots serve the purpose of vegetative increase. The same end is attained by the gemme, which are of many different forms. In Ancura individual cells detach themselves from the thallus and grow up into new plants. In the Marchantie the gomma are formed in peculiar receptacles which stand on the upper side of the ribbon-shaped thallus. In Marchantia polymorpha these receptacles have the form of a basket open at the top, while in Lunularia the margin of the same receptacle is semicircular. The gemme, which are developed on the base of the receptacle, are flat upright cellular bodies, with two indentations at the sides, out of which at a later period, at the time of germination, proceed two growing points. The gemmæ, however, are of similar structure on both sides. Which side is at the time of germination to become dorsal with stomata and air-chambers, and which ventral with root-hairs, is decided by its position with respect to the light. It is always the side turned towards the light which develops itself into that which bears stomata. This occurs even when gemma that swim on water receive light only from below. In that case the under side becomes that which possesses stomata and the air-chambers described above, while the upper side develops root-hairs (rhizoids). Blasia pusilla has also very peculiar receptacles for gemma, provided with a long channel leading outwards, while in many foliose Jungermannica-for example, Jungermannia ventricosa, Scapania nemorosa, Jungermannia bicuspidata, and others-gemma consisting of a few cells are formed on the leaves or the stem respectively. . (2) The Organs of Sex.-The antheridium in Liverworts is a spherical or ellipsoidal cellular body with a shorter or longer stalk (fig. 5, C), and consists of a wall-layer and an interior tissue, the mother-cells of the spermatozoids. In each of these cells a spermatozoid is formed, and, as it appears, in the following way :the peripheral layer of the cell-nucleus becomes thickened, and splits up into a ribbon, either annular or rolled up spirally. The cilia by means of which the spermatozoid moves in water appear, on the other hand, to be formed from the protoplasm in which the cell nucleus lies. The process, however, requires still closer investigation. Each antheridium is originally a simple cell, which grows by repeated subdivision and becomes the antheridial body. By the swelling up of the walls of the spermatozoid mother-cells, the cells of the antheridium-wall are forced asunder at the apex, and the spermatozoids, each imbedded in mucilage, are emitted in jets either free from one another or united into a pulp. This pulp is often ejected by an explosion of the antheridium, as may be easily observed in Frullania dilatata. In water the spermatozoids isolate themselves, and in the most favourable cases are carried over to the archegonia. Since very many spermatozoids are formed in one ntheridium, and since one or very few of these suffice for the FIG. 5.-Marchantia polymorpha. A. Anterior portion of a thallus, 4, with two erect antheridial inflorescences hu. B. Longitudinal vertical section through a young antheridial inflorescence. The antheridia are situated in depressions of the upper surface. b, scales; h, roots (rhizoids); o, e, the openings of the depressions in which the antheridia lie. C. A nearly mature antheridium; st, its stalk; w, the wall. D. Two spermatozoids, magnified 800 diameters. Each possesses two fine cilia. (After Sachs.) diœcious. In the latter case the antheridia and archegonia are found on different individual plants, as in Sphærocarpus terrestris, where the male plant is smaller than the female. În the former case the antheridia and archegonia are found on the same plant. In the thallose forms they are always inserted on the dorsal side of the thallus, and commonly sunk into a cavity in it (fig. 5, B). In Anthoceros the antheridia even stand in closed cavities, which do not open till the antheridium is mature. The organs of sex stand either on ordinary branches, which at a later period vegetate and grow, or on special sexual shoots. These are of especially remarkable construction in the Marchanties, of which Marchantia polymorpha may serve as an example. In this species the antheridia are found on the upper side of a peltate radially-lobed disk, supported on a stalk (fig. 5, 4). The archegonia stand on the under side of a similar receptacle. These structures may be termed "inflorescences." They are not simple branches, but systems of branches which have arisen from the repeated bifurcation of thallus-shoot. Each indentation in the disk of the "inflorescence corresponds to the vegetative point of a branch, and this explains the fact that the oldest antheridia are found in the centre of the disk; and from this point to the periphery, where the vegetative points are found, are successive groups of antheridia of younger growth, for the youngest organs of sex always stand next to the vegetative point of the shoot. The stalk of the inflorescence is nothing else than the inferior portion of the branch-system greatly prolonged. In the leafy Jungermannies the distribution of the organs of sex is also either monoecious or dioecious. The archegonia in this case stand either singly (Lejeunia, &c.) or in larger groups. The first archegonium always arises from the apical cell of the shoot connected with it, so that with it the latter closes its longitudinal growth. This circumstance has been employed in the classification of the foliose Jungermannies (with the exception of Haplomitrium) as acrogynous in contradistinction to the anacrogynous, in which latter the archegonia never proceed from the apex of the shoot itself. Whilst the archegonia of the thallose forms are protected by being lodged in an excavation of the thallus, or surrounded by a luxuriant growth of its tissue, the archegonia of the foliose Jungermannies are enveloped by the leaves of the stem-bud, which on that account are termed perichatial leaves (folia perichetialia), or, collectively, perichæ tium. Between these perichatial leaves and the archegonia there grows up in most forms a second involucre, of a goblet or pitcher shape, the "perianthium" (fig. 4, B). It springs up in the form of a circular fence, gradually growing upwards. In many Jungermannies (Calyrogeia) the archegonia are enclosed in a kind of sack-shaped structure, which forces its way into the ground, in which, in fact, it takes root. This "fruitsac" in the Jungermannica geocalycess is the hollowed-out shoot from which the archegonia arise. Its extremity becomes thickened and forms a circular fence about the archegonia; thus there arises a structure about two twenty-fifths of an inch long, which is constantly becoming deeper, and at the bottom of which the archegonia are placed. There is always an endeavour to protect and envelop the archegonia. This is notably conspicuous in the Marchanties, where round every archegonium there grows after of archegonia is also enveloped by two scales, which incline towards each other like the valves of a mussel-shell. fertilization a special goblet-shaped involucre, whilst every group | In the Jungermannies, when the sporogoniura attains maturity, the stalk becomes very considerably lengthened, the ventral part of the archegonium, which had hitherto kept pace with it in growth, flies asunder, and the capsule emerges. This opens in various ways. In the Jungermannies the wall breaks up into four valves (fig. 4). The sporogonia of Anthoceros behave in a very peculiar manner. The period occupied by their development is much longer than that of the Jungermannies. While they are discharging mature spores at their apex they are still growing at their base, and forming new spores. The sporogonium dehisces by two valves, and is traversed in the middle line by a longitudinal string of cells not employed in the formation of spores. This persists till the maturation of the sporogonium as a little column, and is termed the "columella" (see fig. 7, D). The cells from which the mothercells of the spores proceed have here the form of a dome and enclose an inner portion which becomes the columella, while the inferior portion of the embryo becomes its foot. In Dendroceros, a foreign form of Anthoceros, it drives tubules resembling roots into the tissue of the plant on which the sporogonium is seated. There is no want of transitional steps between this method of formation of the sporogonia and that of the Jungermannica. The species Notothylas is especially noteworthy in this respect. .6-Marchantia polymorpha. Archegonia at different stages of develop ment, in longitudinal section. (1) An erokonium not yet open; its neck portion is still covered at its point by the lid-cells d. In the ventral portion lies a large cell, which has divided into a small upper cell, the "ventral canal-cell," b, and a lower one, the oosphere. In (2) the neck portion of the archegonium is open; the oosphere has assumed a spherical form; the ventral canal-cell is shrivelled up. (3) A fertilized archegonium; the oosphere has become developed into an embryo, here consisting of eight cells: d is an involucre, which in Marchantia grows round the archegonium aiter fertilization (After Sachs.) (3) Development of the Asexual Generation of the Sporogonium.Just as in the vegetative classification we are led in a contin 1ous series from the simple thallose forms to the foliose forms, so in the perfecting of the fertilized oosphere into an embryo (here the sporogonium) there is a gradual advance from simple to more complex forms The first result of fertilization always is that the oosphere becomes surrounded by a membrane, grows, and transforms itself by division into a cellular body. In the simplest case, in Riccia (fig. 7, 4), the only differentiation which takes place in this cellular body is that it forms a walllayer which is soon reabsorbed, while the whole of the interior cells form spores in such a way that by division four spores proceed from every mother-cell. In Marchantia (fig. 7, B) we find a separation taking place in the embryo, in which its inferior portion (that beneath the line 1, 1) becomes the short stalk of the aporogonium and its superior portion becomes the capsule. In the Jungermannies Fio. 7.-Young embryos of Liverworts in longitudinal F. Radula complanata. E shows the arrangement of the (Bg. 7, C, E, F) we find in the young embryo a group of cells I. Jungermannies.-The vegetative body is a thallus without air-chambers, or is a leafy stem. Between these are transitional forms. The sporogonium is differentiated into capsule, stalk, and foot; the capsule dehisces by four valves. (a) Anacrogynous.-The apex is not employed in the formation of the archegonium. To this division belong all the thal lose forms (including Blasia and Fossombronia), as well as Haplomitrium Hookeri. In Riella and Sphærocarpus the capsule is without elaters, but possesses sterile cells morphologically corresponding to them. All the others have elaters. (b) Acrogynous.-The apex or the apical cell itself is employed in the formation of the archegonium. All the forms are foliose, except Haplomitrium, which also, in the development of its leaves, does not correspond with the foliose forms, but with Fossombronia. II. Anthoceroles.-Thallose forms. The archegonia, immediately on their first formation, are sunk into the tissue of the thallus. The antheridia stand in closed cavities. The formation of the that the conveyance to the stem of the matter formed in the leaf takes place. In the species of Polytrichum the middle nerve occupies the greatest part of the leaf, and is covered with lamellæ, which consist of cells bearing chlorophyll. Instead of these lamelle, we find in some other Mosses simple rows of cells, as in Pharomitrium subsessile. A peculiar structure of the leaf is also found in Leucobryum glaucum and Sphagnum. The first-named Mose forms thick greenish-white turfs in damp spots. A transverse section through a leaf shows it to be composed of two (or sporogonium shows no distinction between stalk and capsule, but is three) layers of cells. Above and below is a layer of large pod-shaped and fixed by its swollen foot into the thallus. At cells devoid of contents, the membrane of which is permaturity the sporogonium opens with two valves, between which forated in various places, so that the cavities of the indithe columella becomes visible. At its base it possesses a long and vidual cells communicate with each other; thus arises a permanent growth. system of capillary tubes which suck up water and retain it like a sponge. Between the angles of every two of these colourless cells we find inserted a cell containing chlorophyll. The colourless cells are filled with air instead of water, and thus the whole plant has a whitish appearance (Leucobryum), while the green hue comes out at the approach of moisture. The leaves of Sphagnum possess a similar structure. In these too are perforated cells devoid of contents, and surrounded by the meshes of cells containing chlorophyll. The inner wall of the empty cells devoid of chlorophyll is for the most part set with peculiar thickenings of annular or spiral form (fig. 9, f), which give II. MOSSES (Musci or Musci Frondosi). The Mosses proper play a much larger part in the economy of nature than the Liverworts; they occur in much greater quantity and are more widely distributed, the conditions of their production not being confined within such narrow limits. While the Liverworts, for the most part, thrive only in localities that are not too dry, though some forms that grow upon bark, such as Radula and Frullania, can even endure drought, Mosses, on the other hand, have an almost ubiquitous character. Many grow in water (Conomitrium, Fontinalis, &c.), in swamps (various kinds of Hypnum and others), on dry rocks (Grimmia, Andreæa), on roofs, in fields, and on trees,-in short, under favourable circumstances, a growth of Mosses develops itself almost everywhere. This is connected with the fact that very many have the capacity of enduring drought, and of suspending their growth while it continues and resuming it again in moist weather. Besides, a few, such as Hypnum cupressiforme, Ceratodon, Barbula ruralis, can grow upon any kind of substratum. Others grow by preference on organic substrata: as Buxbaumia indusiata on decayed trunks, Splachnum on old cowdung or on a damp humussoil, Orthotrichum and the species of Neckera on the firm bark of trees, Phascum in manured fields, a great number like Grimmia and Andreæa on rocks. As regards the chemical quality of the substratum, we can distinguish between Mosses that live on chalk (Seligeria, the species of Gymnostomum, and some Hypna) and those that avoid chalk (Andrexa, Dicranum). The species of Polytrichum and Thuidium abietinum are fond of sandy soils, Ephemerum, Fissidens taxifolius, and others of loamy soils, while Archidium phascoides grows on muddy ground. This wide extension of the Leaf-mosses is rendered possible by their uncommonly great capacity for reproduction. Not only is the formation of spores in most species very extensively carried on, but we have to add to this the manifold production of asexual means of multiplication, such as gemmæ, &c. The sexual as well as the asexual generation of Mosses attains to a higher grade of perfection than that of Liverworts. (1) The Sexual Generation.-The extent of the sexual generation of the Moss-plants proper varies within wide limits. While the stem of Ephemerum and some species of Phascum appears in the form of a small bud, often scarcely visible to the naked eye, there are species of more than 4 inches in length, as Sphagnum, Fontinalis, and the tropical species Spiridens. In every case, however, we have here a really leafy stem; no thallose forms exist. The leaves are simple and always small. They either consist of one layer in their whole extent, or are traversed by a mid-rib of several layers, which is often of rather complex structure, and consists of thick-walled and thinwalled tissue-elements, of which the former give mechanical firmness to the leaf, while it is principally in the latter FIG. 9.-Sphagnum acutifolium. A. A part of the surface of the leaf, seen from above. It consists of tubular cells containing chlorophyll cl, and large empty cells, which are thickened on their inner surface by spiral bands f and pierced in some places with openings . B. Transverse section of the leaf; cl, cells containing chlorophyll; ls, the large empty cells. (After Sachs.) it the necessary firmness, as in the vessels of higher plants. In this case too the empty perforated cells are intended for the purpose of absorbing water; and the same end is attained by cells of similar structure, which form the rind of the stem. The stem of Mosses is distinguished by its slight but uniform thickness, which for the most part does not exceed that of a thick thread. Compared with this delicacy, the compact, firm, and tough quality of the corre sponding forms in higher plants is so much the more striking. It depends on the fact that the exterior layers of cells in the stem have thickened cell-walls, generally of a brown colour, while the central parts have thin walls. The differentiation of the tissues reaches its highest point in Polytri chum, Hookeria, Splachnum, and others. Strings of separated cells pass from the leaves into the stem, and apply themselves to its central tissue, which is of different conformation from the rest of the tissue of the stem,-a circumstance which requires mention because this is the first indication of the fact of such extensive occurrence among "vascular" plants that the vascular bundles which | stands on the tip of a side-branch, and the growth of the run off from the leaf pass into the stem and there apply principal stem is thus not interfered with by fructification. themselves to others. The stems are thickly set with In many acrocarpous Mosses the stalk dies after fructificaleaves. It is but seldom that these stand in two rows on tion, and the Moss is then an annual, as in many Phascathe sides, as in Fissidens, Conomitrium, and the sterile ces. In those acrocarpous Mosses which are perennial the shoots of Schistostega. The last-named plant is of special further development is taken up by a side-branch, and a interest as possessing two kinds of shoots of totally differ- so-called " innovation" is ent appearance. The fertile ones have their leaves placed formed. By the dying away on all sides of the stem in a spiral manner; the sterile of the principal stem, these ones, on the other hand, have leaves placed on two sides, innovation-shoots become at and have the appearance of a fern-leaf. This position, a later period independent however, only comes to pass through a shifting and twist- plants. The roots consist of ing of the stem. Originally, in the bud, the leaves of the simple rows of cells, springsterile stems stand in a spiral line. On examination of ing from the surface of the the end of the stem it is found that the growing point stem, especially at its base from which the leaves arise contains, as in the foliose (see p. 72). Liverworts, an apical cell of the form of a three-sided pyramid with a vaulted base. By means of partition walls which are successively parallel to one of the side walls of the apical cell "segments" are cut off; and from each of these proceeds a leaf, as well as a part of the rind of the stem and of the inner tissue. On the direction of the partition walls in the apical cell depends likewise the arrangement of the leaves. The branches do not spring as in most phanerogamous plants from the axil of a leaf, but from the upper surface of the stem below a leaf, and only out of one of its cells. which becomes the apical cell of the branch. In the relation of the ramification to the general struc Fis. 10.-Longitudinal section through the summit of a small male plant of Fanaria hygrometrica, with antheridia in various stages of development. a is a young antheridium-at its point is a "two-edged" apical cell; b, an antheridium, nearly mature; c, paraphyses, hair-like structures which stand between the antheridia and of which the terminal cells are swollen into a globular form; d, section of leaves through the mid-rib; e, section of leaves Through the leaf-surface (lamina). Magnified 800 diameters. (After Sachs.) ture of the moss-plant two leading classes have to be distinguished-the acrocarpous and pleurocarpous Mosses. In the former the growth of the stalk concludes with the formation of a sporogonium; for the archegonium, out of which the former springs, proceeds from the apical cell itself. In the pleurocarpous Mosses the sporogonium (2) The sexual organs of the Leaf-mosses, the antheridia and the archegonia, in their mature condition correspond in the main with those of the Liverworts, from which, however, they differ somewhat in their development. They occur generally in groups at the extremity of a shoot. Such groups containing, as the case may be, either solely antheridia, or solely archegonia, or a mixture of the two, are termed "flowers." An exception to this condition of the antheridia is found in Sphagnum (fig. 11, 4). Here the antheridia do not stand in groups on the summit of the male branch, but are arranged along it, so as to stand beneath the leaves on the prolonged axis of the Fio. 11.-Sphagnum acutifolium. A. A male branch partially deprived of its leaves to show the antheridia a. B. An open antheridium, very highly magnified. C. A mature motile spermatozoid. (After Schimper.) St shoot. In the rest of the Fio. 12.-Longitudinal section through the (fig. 12). They originate, as do the antheridia, from a single cell. cal (3) The development of the fertilized oosphere into the sporogonium differs considerably from that of the Liverworts, both as regards the external processes of growth and as regards the differentiation in the interior of the embryo. In the first of these points the greatest resemblance to the Liverworts is exhibited by Sphagnum. Here the sporogenium continues almost till maturity to be enclosed by the ventral portion of the archegonium-the calyptra,--which keeps pace with it in growth, and which is. irregularly ruptured by it at the period of maturity. Archidium, one of the Phascaces, behaves similarly. In all the other Mosses, however, the sporogonium at an early period bursts through the ventral portion of the archegonium, tearing off the calyptra at its base and raising it up as a cap. The sporogonium possesses a stalk which grows up gradually, but which in Sphagnum, Andreæa, and Archi dium is very short. In the two first-named genera the shortness of the stalk is made up for by a stalklike elongation of that portion of the stem on which the archegonium is placed. Thus arises a false stalk, a "pseudopodium," which is to be distinguished from the real stalk, which belongs to the sporogonium. The capsule is often of complex structure. In the Bryines it possesses a distinct epidermis, often provided with stomata, which is altogether wanting in the vegetative parts of Mosses. A few layers of cells are united to the epidermis, and together with it form the wall. The interior tissue is never entirely employed in the formation of spores, but a part of it remains as a sterile cell-body-the columella (fig. 13, co) -with the exception of Archidium, which in this respect approaches the Liverworts. The embryo, the oides. young sporogonium, is originally fusiform (fig. 14, B, C), and is differentiated into capsule and stalk (seta). The latter commonly penetrates into the tissue of the fruit - shoot, which forms, outside the base of the sporogonium, an exuberant growth like a fence the "vaginula ""-on which we not unfrequently find archegonia sporium) are marked e; co, that have miscarried (fig. 13, v). Fia. 13.-Longitudinal section through a half-developed sporogonium of Phascum bry(The cells are not shown.) The sporogonium has torn away the ventral portion of the archegonium upper part of the archegonium as a cap (calyptra; cal in fig.). Beneath the calyp tra is the capsular portion of the sporogonium. In its walllayer there has been formed an annular intercellular space a, filled with air. The cells from which the mother-cells of the spores proceed (archecolumella; b, endotherium; h, neck of archegonlum; i air-space; s, stalk of the sporogonium (seta); v, vaginula; leaves of the shoot that bears the archegonia. Mag from its base and lifted the nified 60 diameters. In Mosses, as in Liverworts, the spores proceed from the division of one mother-cell into four parts. The phenomena of their germination are very peculiar. In the great majority of the Mosses there arise from the germinating spore cellular filaments resembling Confervæ. They have quite the appearance of Algae, and formerly were even confounded with them. They bear the name of protonema, and often form a thick green covering on the ground in forests. Such a protonema consists of two parts: one above and the other below the ground. Both are rows of cells, but those above the ground contain chlorophyll and have transverse walls placed rectangularly, while those below the ground contain no chlorophyll and their transverse walls are placed obliquely. They serve as roots for the protonema, and of similar structure are the roots (rhizoids) which spring from the On surface of the leafy stem, especially from its base. this protonema, and especially from the basal cells of the threads which are above ground, the moss-stem is formed. This originates from A an outward pouching of one of these cells, and this becomes the apical cell of a mossstem. Several mossplants may be formed on one and the same protonema, which has itself proceeded from one spore. The spores of the Bog(Sphagnum) moss form quite another kind of pro-embryo when they germinate on damp earth. They then transform themselves into an intricately ramified expansion or cell-surface; and any cell of this surface may then become the apical cell of the stem, When they germinate in water the spores of Sphagnum form a thread-like FIG. 14.-Funaria hygrometrica. A. Rudiment of pro-embryo. In the sporogonium or embryo ff', in the ventral some other Mosses cellular body, showing at its point a large "twoportion of the archegonium. The embryo is a too, especially An- edged" wedge-shaped apical cell, which forms segments on the right and left. B and C are dresa, Tetraphis, further stages of development of the sporogoand Diphyscium, renium f, and of the calyptra e. The inferior portion of the embryo has penetrated into the tissue markable forms of of the shoot. h, neck of the archegonium. pro-embryo occur, which, however, can only be alluded to here. In no case does a moss-spore grow directly into a moss-stem. W h Α FIG. 15.-Funaria hygrometrica. A. Germinating spores; e, vacuole; o, root; 8, exosporium. B. Part of a developed protonema, about three weeks after germination; h, a procumbent primary shoot with brown wall and oblique septa, out of which arise ascending branches of limited growth b; K, rudiment of a leaf-bearing axis with root w. A is magnified 550, B about 90 diameters. Mosses propagate themselves very extensively, not only by means of spores, but in a vegetative way. Every one of the hair-shaped roots (rhizoids) which spring out of the stem has the power, when exposed to the light, of forming protonema, and moss-buds upon this. On this depends the fact that the Mosses which grow on tiled roofs (Grimmia and others) are hardly to be extirpated. Even if the turf is removed, the roots that have made their way |