Jan., 1905.] 



Heterosporous Pteridophyte. 





have been unable to adapt themselves to the new condition of 

 things. The next higher subkingdom, the Gyninospernis, be- 

 came the dominant group of plants. 



In tracing out the life cycle, Selaginella kraussiana will be 

 taken as a representative with incidental references to other 

 types. There is, of course, a well-marked alternation of genera- 

 tions, the gametophyte and the sporophyte, and each generation 

 usually leads an independent existence for at least a part of its 

 life. The conspicuous plant is the sporophyte or nonsexual gen- 

 eration. It consists of a more or less dorsi ventral leafv shoot 



Fig. 1. Diagram of Life Cycle of Selaginella. 



from the lower side of wdiich dichotomously branched roots grow 

 out. The roots strike ground usually after growing an inch or 

 more in length. In this plant there is no increase in thickness of 

 the stem but some Heterosporous Pteridophytes do grow consid- 

 erably in thickness by the development of the general tissue but 

 not by a true cambium layer. The vascular bundles are con- 

 centric with the xylem in the centre. The stem usually has two 

 bundles side by side each contained in a tubular cavity or air 

 space and connected with the walls of the cavity by means of 

 numerous slender filaments. Other types have a diJJerent stem 

 structure. 



After attaining a considerable size the sporophyte begins to 

 reproduce by developing cones or primitive flowers at the ends of 

 some branches. The cones are bisporangiate, having two sets of 

 sporophylls which are but slightly differentiated from the ordi- 

 nary foliage leaves. The two kinds of spore-bearing leaves are 



