Page:Encyclopædia Britannica, Ninth Edition, v. 17.djvu/85

MOSSES.] MUSCINE^E 73 into the pores of the tiles still survive, and develop pro- tonema, and new moss-plants upon this. In Phascum and Ephemerum, which are apparently annual Mosses, the pro- tonema is perennial, and forms new plants in the following year. Gemmae also arise in abundance on the protonema (e.g., of the species of Jlarbula) cellular bodies which are surrounded by a dark-coloured membrane, and whose cells are densely filled with a store of material. They are able to endure drought, and on germinating they either form moss-buds directly or protonema in the first place. Pro tonema may also proceed directly from the cells of the leaves and stems of moss-plants, and thus subserve their multiplication. Portions even of the sporogonium may transform their cells back into protonema. If we cut off young sporogonia and place them in damp sand, there will arise from their interior cells (or the wall of the capsule) threads of protonema, on which new plants spring up. Many Mosses also possess special gemmae. In Tetraphis pellucida they are stalked cellular bodies, enveloped by a leafy calyx, from which at a later period they fall away. In Aulacomnium androgynum they spring from the ex tremity of a leafless prolongation of the stalk, in Grimmia Hartmanni and Barbula papillosa from the leaves, &c. CLASSIFICATION OF MOSSES. 1. Sphagnaccie. The Turf -mosses are characterized as well by their anatomical structure as by the development of their sporo gonia. The stem, which at first is unbranched, possesses roots only in its earliest stage. The stems then stand in a thickly-set turf, and receive water through the whole of their surface. The ramification is very abundant. Two kinds of brandies are formed in the terminal buds long whip-shaped " flagellre " which hang down, and whose duration is annual ; and besides these there is formed every year, after the fruit has reached maturity, a side shoot called an "innovation," which acts in the same way as the main stem, and at a later period becomes an independent plant. The sexual organs, antheridia and archegonia, are developed on the side branches. The peculiar structure of the leaves has been already mentioned. That of the stem is analogous to it. The latter possesses a rind, formed out of cells with thin walls, whose protoplasmic contents have completely disappeared. Like the empty cells of the leaf, they are penetrated by openings, and thus form a system of narrow capillary tubes which stand in connexion with each other and open outwards, and through which the water mounts upwards. The branches that bear the male "flowers" make an approach to those of the Liverworts in the fact that the antheridia do not stand on the summit of the shoot, but singly close to its leaves. On the other hand, the archegonia agree in their position and deve lopment with those of the other Mosses. The embryo the j oung sporogonium is at first a pear-shaped body of cellular tissue, the basal portion of which penetrates deeply into the soft tissue of the fruit-branches on which the archegonium is seated. The sporo gonium differs considerably from that of the other Mosses. Those cells which give origin to the mother-cells of the spores termed col lectively " archesporinm " form a dome-shaped layer in the upper portion of the embryo ; thus they are not traversed by the sterile cellular tissue, the columella. Each mother-cell is divided as usual into four spores. The short stalk of the capsule extends itself at maturity only so far as to cause the sporogonium to break through the calyptra, the place of a stalk being practically supplied by the " pseudopodinm." l The pro-embryo is a cell-surface. 2. The A ndreseaceK are small blackish Mos*ses growing on rocks. Their antheridia resemble those of the other Mosses. The develop ment of the embryo is anomalous. The archesporium is, as in Sphagnum, a, dome-shaped layer of cells. On the extremity of the mature capsule is placed the calyptra, which has been torn away, as a delicate cap. The mode of dehiscence of the capsule here reminds us of the Liverworts. This takes place by four longitu dinal clefts, which allow the exit of the spores, and are open in dry and closed in damp weather. In this group also the stalk of the sporogonium remains short, its place being supplied by a pseudopodium. " 3. The Phoscaccae, which are small and generally annual Mosses, are distinguished from the following division by the fact that the capsule does not open by separation of a lid, but remains closed, and the spores are not set free till the wall of the capsule decays. A remarkably anomalous form is Archidium ; the development of 1 The possession of an elastic stalk has this advantage for the sporo gonium, that it promotes the scattering abroad of the spores by means of the wind. its embryo reminds us of that of the Liverworts ; the mature sporo gonium also possesses no calyptra, but breaks through the ventral portion of the archegonium like that of Spluignum and that of the Liverworts. The Phoscacese are termed cleistocarpous " in con tradistinction to the " stegocarpous " Mosses. 4. The Bryincse comprehend by far the greatest number of all the species of Mosses. They are characterized above all by the structure of their sporogonia. Here the parts of the latter are always the longer or shorter bristle - shaped stalk (seta), the capsule, and the calyptra carried up on its summit. That part of the stalk where it passes into the capsule is termed apophysis ; on its epidermis, as well as on that of the capsule, we almost always find stomata. As regards the structure of the capsule, at a very early period a space filled with air makes its appearance, which divides the interior mass from the wall, which is composed of several layers. This interior complex mass of tissue consists of those cells which give rise to the mother -cells of the spores (the archesporium), of a few layers of cells which surround these only externally, and of an inner mass of tissue, the columella. The latter, however, passes in this case through the cells of the archesporium ; these latter form, as in the Phascaceas, a stratum of cells which has the form of a barrel, open above and below (fig. 13), and encloses the columella. The Bryinese are also char acterized by the way in which the capsule opens. The upper part of the wall of the capsule is in this case always thrown off as a lid (operculum). This happens in one of two ways : either a layer (or several layers of cells lying upon one another), placed between the inferior portion of the capsule and the operculum. forms a ring (annulus), the cell-walls of which become thickened and partially swollen, so that the annulus becomes loosened and thus causes separation of the opercnlum and the capsule from each other, or there remains simply a thin-walled annular zone of cells belonging to the wall of the capsule, which splits asunder in dry weather, "yhen the operculum falls away the margin of the open capsule appears in most cases set round with a single or double ring of tooth-like formations, which are termed peristome. This is wanting in Gymnostomum and Hymcnostomum. It occurs in its simplest form in Tetraphis. Here the epidermis of the upper conical portion falls off as an operculum, while the whole tissue that lies beneath splits crosswise into four valves, which form the peristome. In the other Mosses, with the exception of Poly- trichum, the teeth of the peristome have an essentially different origin. They are in fact nothing but the thickened portions of cell - membranes, whose nnthickened portions have per ished and been torn asunder. Fig. 16 shows a portion of a longitudinal section through the upper part of the capsule of Funaria hygromct- rica. The capsule pos sesses a brown epider mis e, whose walls are greatly thickened ; sc is the tissue that lies between the epi dermis and the air spaces h, I of the cap sule; sthemother-cells of the spores, and farther inwards follows the columella. Im mediately above the air-space rises the stratum of cells which forms the peri stome, of one tooth of which a longitudinal section is given in fig. 16. It arises from the great thickening of the outer side of the walls of a row of superposed cells. At maturity the upper FIG. 16. Part of a longitudinal section through the nortirm of thp wall upper part of a capsule of Fvnaria hygrometrica. portion I vail A ^ an ^ oare the t( th of the peristome ;t, pointed cells. (After Sachs.) of the capsule falls off as an operculum, the cells marked _p disappear, and only the thickened parts of the cell- membranes remain as the teeth of the peristome. In Funaria and in other cases the peristome is double, for those cell-walls (fig. 16, i) XVII. 10