4o6 



MOSSES AND FERNS 



CHAP. 



spermatozoids collect in equal numbers about those which are 

 still closed, and even about spores that have not germinated 

 at all. Marsilia did not prove a good subject for studying 

 the behaviour of the spermatozoid within the &^^, owing to 

 the difficulty of differentiating the spermatozoid after its 

 entrance. Pilularia is better in this respect, and shows that 



Jig. 212. — Marsilia vestita (Hook and Grev.). Development of the embryo. A, Longitudinal 

 section of archegonium with two-celled embrj'o ; B, similar section of a later stage ; C, two 

 transverse sections of a young embryo ; D, two longitudinal sections of an older one ; I, I, the 

 basal wall; L, cotyledon ; st, stem; r, root ; F, foot. A-C, X 525 ; D, X260. 



the changes are the same as those described in Marattia and 

 Osmunda. 



Coincident with the first divisions in the embryo, each 

 of the lateral cells of the prothallium (venter) divides by a 

 pericHnal wall, but the basal layer of cells remains but one cell 

 thick. The prothallium grows with the embryo for some 



