LEPTOSPORANGIATM HETEROSPORE^ 



423 



developed. A noticeable difference is the segregation of the 

 protoplasm containing the nucleus, which occupies the apical 

 papilla. This is filled with fine granules, but is entirely free 

 from the very large starch grains of the large basal part of the 

 spore. The nucleus is somewhat flattened. A similar arrange- 

 ment of the spore contents is found in Pilularia, but the apex 

 of the spore does not form a distinct papilla. The epispore is 

 of nearly equal thickness, except at the extreme apex, in Mar- 

 silia, but in Pilularia, especially in P. globulifera, the epispore 



Fig. 248. — Marsilia vestita. Germination of the macrospore; A, longitudinal section of 

 the ripe macrospore, X6o; «, nucleus; B-G, successive stages in the development of 

 the female prothallium and archegonium, X360; C, E, transverse sections, the 

 others longitudinal; n, neck canal cell; h, ventral canal cell; /, receptive spot of 

 the egg; k, remains of the nucleus of the spore cavity. 



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 cuts off the mother cell of the prothallium; but in Mar- 

 silia, while this is usually so, occasionally a lateral cell is cut 



