382 STRUCTURE AND LIFE HISTORIES 



Lycopodium lucidulum (which is common in the northern 

 United States), and are borne near, but not in, the axils 

 of the leaves. A young rootlet commonly appears on the 

 gemma while it is still attached to the plant. After it 

 falls off, the axis elongates, and a new sporophyte is 

 formed, like the old one. 



342. Life History. — The student should be able to make 

 his own diagram of the life history of Lycopodium, fol- 

 lowing the examples given in connection with forms 

 previously studied. 



m. LITTLE CLUB-MOSSES (SELAGINELLALES) 

 SELAGINELLA (LITTLE CLUB-MOSS) 



343. Habitat and Distribution. — The little club-mosses 

 (species of Selaginella) are found in every continent and 

 on most of the larger islands. They usually grow only in 

 moist situations, and are very common in conservatories, 

 under the plant benches, and in pots and hanging baskets. 



344. The Sporophyte. — The plant body (sporophyte) 

 consists of a much-branched stem (Fig. 277), bearing 

 scale-like, but green foliage-leaves, sessile and more or less 

 closely appressed to the stem. At the tips of the branches 

 the foliage-leaves are replaced by sporophylls, so arranged 

 as to form a clearly distinguished cone (Figs. 278 and 281). 

 Near the base of the leaves, on the surface next the stem, 

 is formed a thin, membraneous flap, the ligule (Figs. 279 

 and 280). The possession of a ligule is one of the funda- 

 mental distinguishing characteristics of Selaginella. 



345. Two Kinds of Spores. Heterospory. — If we 

 examine a longitudinal section of a cone, we shall normally 

 find a sporangium in the axil of each sporophyll. In 

 exceptional cases the lower or basal leaves of the cone are 



