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Bryophyta

Bryophyta, or Muscineae, one of the main divisions or sub-kingdoms of the vegetable kingdom, ranking in any linear treatment next above the Thallophyta, or Algae and Fungi, and below the Pteridophyta, or ferns and fern-allies. They agree with the Thallophytes in having only cellular tissue; but many cells in the leaves and stems of Sphagnum and some other mosses have spiral thickening-bands, as have also the remarkable long fusiform cells known as "elaters," which occur with the spores in most Hepaticae, or liverworts. The leaves of mosses have also a long central cell foreshadowing the midrib, and in some of the higher forms there is also an axial strand resembling the procambium of vascular plants. Though the leaves of hepatics and of most mosses are only one cell thick, a distinct "epidermis" with "stomata" or transpiration-spores is differentiated on some moss-capsules. The marked distinction between stem and leaf separates the Bryophyta from almost all thallophytes, though in the Marchantiaceae, or liverworts proper, the stem is thalloid. Growth by "innovations," or new shoots becoming detached by the decay of their bases, is common among bryophytes, as among algae; whilst the asexual production of "gemmae," or small groups of cells capable of growing into new plants, is particularly characteristic of the sub-kingdom. The function of roots is performed in this group by simple hair-like bodies, and the leaves never have the complex branching familiar to us in the ferns. From the Pteridophyta the Bryophyta are separated in the most marked manner by the nature of their "alternation of generations." The spore of a bryophyte generally contains chlorophyll, and on germinating on moist earth gives rise to branching green filaments, or protonema, on which buds arise which develop into the leafy plant. The reproductive organs, or antheridia and archegonia, are developed on branches of this leafy plant, which is, therefore, the oophore stage, and not the sporophore or spore-bearing stage, as is the leafy plant in Pteridophyta. The sporophore stage in Bryophyta is a mere insignificant appendage to the oophore, being little more than the so-called "capsule" or "moss-fruit," whilst in Pteridophyta it is the oophore stage, the prothallus, that is small and transitory. The arehegonium in Bryophyta is flask-shaped, with a long neck, and the antheridium is an ovoid or club-shaped body with a wall one cell thick enclosing numerous spermatocytes, or mother-cells, each of which gives rise to one spirally-coiled antherozoid. The antherozoids of thallophytes are not coiled, and those of pteridophytes generally more coiled. The archegonia and antheridia of bryophytes are generally accompanied by barren hair-like bodies or paraphyses and surrounded by special perichaetial leaves. On fertilisation the central cell of the archegonium does not give rise to cotyledon and radicle, as in ferns and flowering plants, but to a mass of cells or embryo imbedded in, but not united to, the tissue of the oophore, which grows into the spore-containing capsule and its stalk or seta. The archegonium is ruptured, forming a cup or vaginule below the seta or a cap or calyptra over the capsule. The classes into which the sub-kingdom Bryophyta is divided are the Hepaticae, or liverworts, the Musci, or mosses, and, perhaps, the Characeaae (q.v.).