THE PTEKIDOPHYTES 293 



some of which is deposited in the rhizome and used in pro- 

 ducing next season's sporophyll branch. In all the other known 

 species of Equisetum the sporophylls grow upon the same branch 

 that does the chlorophyll work. 



269. Equisetum arvense: reproduction. At the tip of the spo- 

 rophyll branch is the collection of sporophylls. Each (Fig. 

 244, (7) has an outer shield-like surface which grows at the 

 end of the sporophyll stalk. From the under surface of the 

 sporophyll the sporangia grow. The spores are peculiarly 

 wound about by elaters (Fig. 244, D and E), which, as they 

 unroll and twist about, may assist in spore distribution. 



These asexual spores germinate almost immediately when 

 ripe, and develop into gametophytes, each one of which pro- 

 duces but a single kind of sex organ ; that is, a gametophyte 

 is male (produces antheridia) or female (produces archegonia). 

 After fertilization the oospore germinates and produces a new 

 sporophyte, thus completing the life cycle. 



THE CLUB MOSSES (LYCOPODINE^E) 



270. This class includes the two genera Lycopodium and 

 Selaginella, though fossils show a former abundance of related 

 genera. Both are very widely distributed and have many 

 species. At Christmas time these plants are often used for 

 decoration and are called "club moss" or "ground pine." The 

 rootstock of Lycopodium often grows upon or just beneath the 

 old leaves, frequently sending upright branches (Fig. 245) 

 into the air. 



Selaginella often has an almost upright stem. Roots may 

 arise from portions of this stem that are in the air. Leaves 

 are spirally arranged. In some of the more prostrate Selagi- 

 nella forms the leaves have become differentiated so as to 

 appear in two small and two large rows. 



271. Reproduction in Lycopodium and Selaginella. At the tips 

 of branches strobili, or cones, are formed in most species 

 by ordinary foliage leaves becoming sporophylls without losing 



