RHIZOCARPAE.
The RhizocarpjE, a group of minute water-plants, are represented by four genera found in different parts of the world, of which the Pillwort and Pepperwort are probably the best-known, these plants being rather botanical curiosities than objects of every-day attention. They are inconspicuous plants, growing in the mud at the edges of pools, or floating about in stagnant water. A plant of this group (Marsilea) (Fig. 127) consists of a creeping stem; from the upper side rise stalks ending in leaves, from the lower hang roots; at the base of the stalks, near the roots, are seen the spore-cases (sporocarps): hence the name of this order, Rhizos- (root) carpae (fruit). The spore-cases of the Pill-wort (Pilularia) and Pepperwort (Marsilea) contain both small and large spores. In Salvinia and Azolla the large and small spores have each their special spore-case. The importance of this arrangement of the reproductive apparatus in Salvinia and Azolla will appear when speaking of the flowering plants. The development of the future Rhizocarp from the large and small spores is the same as that observed in the Club-mosses, to which we will now turn.
LYCOPODIACEAE.
The Lycopodiaceae (Fig. 128), or Club-mosses, are delicate creeping plants, producing leafy-like branches, resembling in their general appearance Mosses, though differing from them in structure and manner of reproduction. The Club-mosses of the present day are small plants; this was not always the case, the order being represented in past time by trees, attaining the height of sixty feet, with gigantic roots, giving the vegetation of that period a very characteristic appearance. The stem of the Lycopodiaceae exhibits the same vascular and cellular structure noticed in the
