XII LEPTOSPORANGIAT.K HETEROSFORE.E .401 



exospore and the epispore or perinium, composed of closely-set 

 prismatic rods. The central nucleus is large and distinct, with 

 usually one or two nucleoli. 



The first division takes place at ordinary temperatures, 

 about 20' C, within about an hour after the spores are placed 

 in water. Previous to this the nucleus enlarges and moves to 

 one side of the spore, usually the point opposite the apex, and 

 the granular cytoplasm collects near the centre and is connected 

 with the peripheral cytoplasmic zone only by thin strands. 

 The first wall divides the spore into two very unequal cells, the 

 smaller containing but little granular contents, and representing 

 the vegetative part of the prothallium, while the upper becomes 

 the antheridium. In Pilularia there is subsequently cut off a 

 small cell from the vegetative cell, and Belajeff^ states that 

 this also is the case in Marsilia, but a careful examination of 

 a great many microtome sections of AT. vestita has failed to show 

 it in that species. 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, being in fact the homologue of the first 

 funnel-shaped wall in the antheridium of the Polypodiaceae (Fig. 



207, D). Sometimes 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 forma- 

 tion of this wall is apparently suppressed here, perhaps as the 

 result of the extremely rapid development of the antheridium, 

 and the separation of the sperm cells takes place by walls cut 

 off from the periphery of the two upper cells. A cap cell (Fig. 



208, d) is almost always present, as in Pilularia and the 

 Polypodiaceae.  



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 infrequently the two groups of sperm 

 cells are completely separated by one of these sterile cells 

 (Fig. 207, F), but this is by no means always the case, 

 and does not justify Belajeff's ^ interpretation of each group 

 representing a separate antheridium. It is simply a more 

 complete separation of the two primitive groups of sperm cells 



1 Belajeff{3), p. 330. 2 Belajeff, I.e. 



2 D 



