420 



MOSSES AND FERNS 



CHAP. 



than in Pilularia (Fig. 245, A, y). The next division is not 

 always the same, but is usually effected by a wall nearly parallel 

 to the first one, but more or less concave (Fig. 244, D). Some- 

 times the antheridial cell divides at once by an oblique wall into 

 two nearly equal cells, from each of which a group of sperm 

 cells is later cut off. In no case was the central cell cut off by 

 a dome-shaped wall, such as is common in the homosporous 

 Ferns, and also in Pilularia. The formation of this wall is 

 apparently suppressed here, perhaps as the result of the ex- 

 tremely rapid development of the antheridium, and the separa- 

 tion of the sperm cells takes place by walls cut off from the 

 periphery of the two, upper cells. A cap cell (Fig. 245, d) is 

 almost always prese/t, as in Pilularia and the Polypodiacese. 



From the two cells of 

 the middle part of the 

 antheridium a varying 

 number of sterile cells are 

 cut off, which are quite 

 transparent, while the 

 contents of the central 

 cells are very densely 

 granular. Not infrequent- 

 ly the two groups of 

 sperm cells are completely 

 separated by one of these 

 sterile cells (Fig. 244, F), 

 and Belajeff considers 

 that each group of sperm 

 cells represents a distinct 

 antheridium. In view of 

 the relationship between 

 the Marsiliacese and Schizasacese, indicated by recent studies 

 on the structure and development of the two families (Camp- 

 bell (26)), this view has some support, as there is a cer- 

 tain resemblance between each of these cell groups and the 

 simple antheridium of Aneimia or Schizcea. The divisions in 

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

 each group are arranged very symmetrically (Fig. 245). The 

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

 from the time germination begins, and the formation of the 

 spermatozoids commences about an hour later and takes about 



Fig. 245. — Marsilia vestita. A, Longitudinal, B, 

 transverse division of the male gametophyte, 

 X400; X, y, the two vegetative prothalHal 



cells; C, two free spermatozoids, X8oo; v, 

 vesicle. 



