[Illustration: FIG. 229.--_Lycopodium annotinum_: _A_ embryo (nat. size), with prothallium (_pr_), one embryo is broken off; _B_ the prothallium (slightly magnified); _C_ section through the prothallium and embryo in the direction _a-b_ of _A_, and vertically in the plane of the paper.] [Illustration: FIG. 230.--_Lycopodium clavatum_: portion of a stem, bearing cones (_a_); _s_ a spore; _h_ sporangium in the axil of a leaf, _s_.] Order 1. =Lycopodiaceæ.= The PROTHALLIUM is only known in a few species at present, but in these it is more or less tubercular, and bears both antheridia and archegonia. In _L. annotinum_ the prothallium is a relatively large mass of cells, without chlorophyll, and subterranean, in which the antheridia and archegonia are embedded (Fig. 229). In the widely distributed tropical species, _L. cernuum_, and in _L. inundatum_, it is a small tubercular body which has a subterranean portion, with either little or no chlorophyll; and an aerial green portion. The prothallia of _L. phlegmaria_ and others live saprophytically in the crevices of the bark of trees; they are partly filamentous, branched, and possess no chlorophyll. The =asexual generation=. PERENNIAL PLANTS. The stem branches monopodially (often apparently dichotomously), and is thickly covered by small, simple, triangular or scale-like leaves. The leaves are spirally arranged in some species (Figs. 229, 230), and in others, whose stem is compressed with unequal sides, opposite (Fig. 231). The roots of _Lycopodium_ are dichotomously branched. The SPORANGIA in _Lycopodium_ are situated singly at the base of the leaves, almost in their axils; they are reniform, unilocular and open like a mussel-shell by two valves (Fig. 230 _h_). The sporangia are developed from a group of surface cells. The archesporium is formed from one hypodermal cell (or perhaps a cell-row). [Illustration: FIG. 231.--_Lycopodium complanatum_: _a_ leaves on the edges of the stem; _d_ leaves on the sides.] [Illustration: FIG. 232.--_Lycopodium clavatum._ A tetrahedral spore seen from above, where the three borders join; and a tetrad of bilateral spores, still lying in the mother-cell.] The fertile leaves are collected upon definite regions of the stem. They are either similar to the barren ones, and then the fertile portions of the stem pass gradually, without any break, into the barren portion (_L. selago_); or they differ from the barren leaves, and are then collected into special apical cones (Fig. 230 _a_). The SPORES are tetrahedral or bilateral (Fig. 232). About 100 species, chiefly tropical.