CHAPTER XVIII. 



BKYOPHYTA. 



434. This division includes plants of a much, greater de- 

 gree of complexity than any of the preceding. In all there 

 is a well-marked alternation of sexual and asexual genera- 

 tions. The first generation that is, the one proceeding 

 from the spore bears the sexual organs, and hence it is 

 called the sexual generation. After fertilization, and as a 

 result of it, there grows a sporocarp, which consists of a case 

 or body, in which spores arise asexually ; hence this is called 

 the asexual generation. From these spores the sexual gen- 

 eration is again produced. 



435. The production of the sexual generation may take 

 place either directly or indirectly. In the first a thallus-like 

 structure is produced directly from the germination of the 

 spore, as in some of the Liverworts (Anthoceros, Frullania, 

 etc.) ; in most Mosses, however, there is first produced from 

 the spore a Conferva-like mass of threads, the pro-embryo or 

 protonema, and upon this buds arise, which grow into the 

 leafy sexual generation. 



436. The sexual organs of Bryophytes consist of arche- 

 gonia and antheridia. The former are flask-shaped bodies, 

 whose walls are composed of a single layer of cells. In the 

 bottom of the cavity of each archegonium is a naked mass of 

 protoplasm, the germ-cell, which is the essential part of the 

 female organ. The antheridia are of various shapes ; but 

 they are generally club-shaped, or somewhat spherical, stalked 

 bodies, whose walls, like those of the archegonia, are com- 

 posed of a single layer of cells. The antheridia are filled 

 with, usually, a great number of sperm-cells, each of which 

 contains a single spirally coiled spermatozoid. 



