106 



EVOLUTION OF PLANTS 



simply lives long enough to produce the sexual organs 

 and to nourish the embryo-sporophyte until it becomes 

 self-supporting. 



THE LIVERWORTS (Hepaticce) 



Like the Confervacese among the green algse, the 

 Liverworts seem to represent a low generalized assem- 

 blage of plants showing 

 affinities with several 

 other groups, and, in- 

 deed, they probably rep- 

 resent the ancestral forms 

 from which have arisen 

 all the higher plants. 

 While the lower HepaticaB 

 are but little more com- 

 plicated than some of the 

 Confervaceae, others show 

 a considerable degree of 

 differentiation of the ga- 

 metophyte. The latter, 

 in the simplest cases (Fig. 

 27, A, C), is a small flat 

 body or thallus composed 

 of almost uniform green 

 cells, the whole fastened 

 to the ground by numerous 

 delicate hairs or rhizoids. 



This thallus grows by the divisions of a definite apical 

 cell, which differs in different genera, or even in differ- 

 ent species of the same genus. 



FIG. 27 (Hepaticae). A, B, C, thal- 

 lose liverworts ; A, Riccia, sp, the 

 very small sporophyte ; B, Cono- 

 cephalus, st, stomata; C, Metz- 

 geria ; D, Blasia, a liverwort which 

 shows the first formation of leaf- 

 like organs, I ; E, Lejeunia, a foli- 

 ose liverwort with definite stem 

 and three rows of leaves, large 

 dorsal ones, and small ventral 

 ones, am. 



