402 



MOSSES AND FERNS 



CHAP. 



which is indicated by the first vertical wall in the central cell 

 of the antheridium of all Leptosporangiatae. The divisions in 

 the central cells are very regular, and the sixteen sperm cells in 

 each group are arranged very symmetrically (Fig. 208). The 

 whole number in M. vestita is completed in about seven hours 

 from the time germination begins, and the formation of the sper- 

 matozoids commences about an hour later and takes about four 

 hours for its completion. The structure of the fully-developed 

 antheridium will be best understood from a comparison of the 

 three different views (Fig. 208, A, B, C). In these figures x 



Fig. 208. — A, B, C, Sections made in three planes of the ripe antheridium of Marsilia vestita., X450 ; 

 jr, vegetative prothallial cell; d, cover cell of the antheridium; D, E, spermatozoids, X900; v, 

 the vesicle attached to the large posterior coils. 



is the small vegetative cell, in the basal cell of the antheridium,/* 

 the lateral wall cells, and d the cover cell. Pilula7'-ia approaches 

 much nearer to the Polypodiacese in the structure of the 

 antheridium (Fig. 209). The first funnel-shaped wall is much 

 more frequently extended to the basal wall, and the two groups 

 of sperm cells are much less distinct than in Marsilia. 



The spermatozoids of Marsilia are at once distinguished 

 by a great number of coils, sometimes thirteen or fourteen in 

 M. vestita. The cilia are very numerous, but are attached only 



