BRYOPHYTES. Among the liverworts the body is either a flat ribbon, more or less branched, or more extended in one direction, producing a band-like form. If branching occurs, it is likely to take place in the plane of the flattening. The branch may be essentially like the main axis, or it may take on a special form. Sometimes the more extended growth occurs in several diree Hums, when the body becomes more or less regu larly lobed. Unequal growth of any part of the flat body will produce a tinted or frilled form.
It is only when the plants become massive, so that sonic cells are exposed on the surface and others hidden in the interior, that marked dis similarity arises. Then the external parts are likely to be differentiated from the internal, be is segmented into a roundish axis with thin, scale-like outgrowths on upper and under sur faces, the upper ones being relatively large, con spicuous, and green. whence they are called leaves; while the under ones are small, incon spicuous, and pole. From various parts of the body on the under side arise hold-fasts in the form of slender hairs (rhizoids). Similar out growths, but of varied form, are not infrequently found on other parts of the body. (See HEPA TIC.E.) In mosses, the body, when young, is a much-branched filament, usually transient, from which there arises a more permanent cylindrical axis, erect, with few branches, or horizontal and much branched, on whose sides are developed green thin outgrowths, the leaves. These are usually a single sheet of cells, except near the middle line. where several layers of cells con stitute a midrib. The shapes of the leaves are extremely varied. See 1\1 uscr.
l'•ERIDOPHYTES AND SPERMATOPHYTES. The gainetophyte of the ferns is a thin, roundish, heart-shaped body, seldom exceeding a quarter of an inch in diameter. and transient. In fern allies
it is reduced to a few cells, and is not visible without microscopic observation. The vegeta tive body, which is long lived, does not bear sex organs as in the lower plants, but gives rise only to non-sexual reproductive bodies of various kinds called spores; whence it is known as the sporophyte. (See ALTERNATION OF GEN ERATIONS.) The external anatomy of the spo•o phyte in the pteridophytes (ferns and their allies) and spermatophytes (seed plants or th»vering plants) is much alike. It is almost without exception segmented into two distinct parts, the root and the shoot. The root is usually much branched, and bears on its newer parts sur face outgrowths called root-hairs. The tips of the branches, at which the growing points are lo cated. are protected by somewhat older cells, which constitute a root-cap. (See 1100T.) The shoot is usually differentiated into a central axis, the stem, with lateral outgrowths of two kinds: ( 1 ) Those having unlimited growth; i.e., branches. which are similar in all essential re spects to the main axis, though they may he spe cialized in form and function. ( Por further de tails respecting the structure of the stem and the forms which it assumes, see STEM.) (2) Seg ments with limited growth, usually flat. thin. and broad ; i.e., leaves, which are developed in a variety of forms. (See LEAF.) Simple out growths of various forms, arising from single cells or small groups of cells. may develop on any part of the shoot as scales. hairs, etc.