Page:Encyclopædia Britannica, Ninth Edition, v. 17.djvu/84

72 MUSCINEJE [MOSSES. -A (fig. 12). They originate, as do the antlieridia, from a single cell. (3) The development of the fertilized oosphere into the sporogonium differs considerably from that of the Liver worts, 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 resem blance to the Liverworts is exhibited by Sphagnum. Here the sporogonium continues almost till maturity to be en closed 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 Phascacess, behaves similarly. In all the other Mosses, however, the sporogonium at an early period bursts through the ventral portion of the arche gonium, 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, Andre fea, and Archi dium is very short. In the two first-named genera the shortness of the stalk is made up for by a stalk- like 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 Bryinex it pos sesses a distinct epidermis, often provided with stomata, which is al together 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. 1 3, co) with the exception of Archidium, FIO. 13. Longitudinal section wlii oh in tVik rp^ripM- jmnrnaplips flip through a half -developed wnicn in tins respect approacnes the Liverworts. The embryo, the 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 sporo gonium, an exuberant growth like a fence the "vaginula" on which we not unfrequently find archegonia that have miscarried (fig. 13, v). 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 re sembling Confervae. 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 proto nema 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 sporogonium ofFhascnm on/- ot</es. (The cells are not shown.) The sporogonium has torn away the ventral portion of the archegonium from its base and lifted the upper part of the archego nium as a cap (calyptra; cal in fig.). Beneath the calyp tra is the capsular portion of the sporogonium. In its wall- layer there has been formed an annular intercellular space a, filled with air. The cells from which the mother-cells of the spores proceed (arche- sporium) are marked c; co, columella; &, endotherium; h, neck of archegonium; i, air-space; s, stalk of the sporogonium (seta); v, vagin- ula; /, leaves of the shoot that bears the archegonia. Mag nified 60 diameters. A surface of the leafy stem, especially from its base. On this protonema, and especially from the basal cells of the threads which are above ground, the moss-stem is formed. This originates from an outward pouching of one of these cells, and this becomes the apical cell of a moss- stem. Several moss- plants may be formed on one and the same protonema, which has itself proceeded from one spore. The spores of the Bog- moss (Sphagnum) form quite another kind of pro -embryo when they germinate on damp earth. They then transform them selves into an intri cately ramified ex pansion or cell -sur face; and any cell of this surface may then become the api cal cell of the stem. When they germi nate in water the spores of Sphagnum form a thread-like pro-embryo. In some other Mosses too, especially An- dresea, Tetraphis, and Diphyscium, re markable forms of FIO. 14. Funaria hygromctrica Rudiment of the sporogonium or embryo // , in the ventral portion of the archegonium. The embryo is a cellular body, showing at its point a large "two- edged" wedge-shaped apical cell, which forms segments on the right and left. Jl and C are further stages of development of the sporogo nium /, and of the calyptra c. The inferior por tion of the embryo has penetrated into the tissue 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. FIO. 15. Funaria hygrometrica. A. Germinating spores; v, vacuole; w, root; s, 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 6; 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