404 



MOSSES AND FERNS 



CHAP. 



Marsilia, but in Pilularia, especially in P. globulifera, the 

 epispore of the upper third is much thicker, and from the 

 outside the spore appears somewhat constricted below this. 



Previous to the first division, which in M. vestita takes 

 place about two hours after the spores are placed in water, 

 the amount of protoplasm at the apex increases, and the 

 nucleus becomes nearly globular and there is an increase in 

 the amount of chromatin. In Pilularia the first wall is always 

 transverse and separates the mother cell of the prothallium ; 



Fig. 2IO. — Marsilia vestita (Hook and Grev.). Germination of the macrospore ; A, longitudinal 

 section of the ripe macrospore, X 60 ; «, nucleus ; B-G, successive stages in the development of 

 the female prothallium and archegonium, X 360 ; C, E, transverse sections, the others longitudinal ; 

 n, neck canal cell ; /^, ventral canal cell ; r, receptive spot of the egg ; k, remains of the nucleus 

 of the spore cavity. 



but in Marsilia, while this is usually so, occasionally a lateral 

 cell is cut off first from the papilla. In Pilularia the next wall 

 is parallel to this transverse primary wall, and this may also 

 occur in Marsilia, but in the latter more commonly the first 

 lateral cell is first cut off by a vertical wall, and this is followed 

 by two others, which intersect it and include a large central 

 cell (Fig. 210, E), from which a basal cell is subsequently 

 separated. In Pilularia, besides the formation of the basal cell 

 by the second wall, the central cell is, as a rule, cut out by two, 



