XI LEPTOSPORANGIAT^ HETBROSPORE^ 401 



dently of advantage in bringing the male and female plants 

 together. 



The macrospores germinate most promptly in the early 

 autumn, and in California, where this species is abundant, this 

 is probably the natural time for germination. As the first 

 stages of germination take place within the completely closed 

 spore, it is difficult to tell precisely just when it begins. So 

 nearly as could be determined, the first division may take place 

 within two or three days, and the whole development be com- 

 pleted within a week. 



A section of the ripe spore, still within the sporangium, 

 shows its contents to be nearly uniform, and much like that of 

 Isoetes. The nucleus is here at the apex of the spore cavity 

 and not conspicuous. It is somewhat elongated and stains but 

 little. No nucleolus can be seen. 



The first sign of germination is an increase in the size of 

 the nucleus, which becomes nearly globular, and a small nucle- 

 olus becomes evident. At the same time the cytoplasm about 

 it becomes free from large granules and indicates the position 

 of the mother cell of the prothallium. This upper part of the 

 spore cavity is now cut off by a nearly straight transverse wall, 

 and this small lenticular cell becomes the prothallium. The 

 granules in its cytoplasm are finer than those in the large basal 

 cell, and the nucleus stains strongly and shows a large nucleolus. 

 The nucleus of the lower cell remains in the upper part, and is 

 much like that of the prothallial cell. 



The first division wall in the upper cell is vertical and di- 

 vides it into two cells of unequal size. In a prothallium having 

 but three cells, the second wall was also vertical, but in others it 

 looked as if it were horizontal, which Prantl ((4), p. 427) 

 states is the case in Salvinia. From the upper of the cells 

 formed by the first horizontal wall the first archegonium arises. 

 If the horizontal wall forms early, the primary archegonium is 

 nealy central, but if two vertical walls precede it, its position is 

 nearer the side opposite the first cell cut ofif. In the few cases 

 where successful cross-sections of the very young prothallium 

 were made, the archegonium mother cell was decidedly tri- 

 angular, showing that it was formed by three intersecting walls, 

 as in Isoetes. It divides into an outer and inner cell, the latter, 

 as in Isoetes, giving rise at once to tgg and canal cells, with- 

 out the formation of a basal cell. 

 26 



