Class 3. Lycopodinæ (Club-Mosses).
The characteristics of this class have been given on page [205]. It consists of two sub-classes, one embracing isosporous, the other heterosporous forms.
Sub-Class 1. Lycopodieæ (Isosporous Lycopodinæ).
One kind of spore. Prothallium large, partly green. Leaves without ligule.
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.
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.