XIV ISOETACEAi 539 



but in /. cchinospora var. Braunii the surface of the spore is 

 nearly smooth. In this species the spores beg-in to ripen in the 

 early autumn, and continue to do so as long as the conditions 

 permit of growth. The spores are set free by the decay of the 

 sporangium wall, which probably in nature is not completely 

 the case until winter or early spring, which seems to be the 

 natural time for germination. If they are set free artificially, 

 however, they will germinate promptly, especially if this is done 

 late in the autumn or during the winter. Thus spores sown in 

 December produced free spermatozoids in two weeks. The 

 spores do not all germinate with equal promptness, and all 

 stages of development may be met with in the same lot. The 

 ripe spore has no chlorophyll, but contains besides the nucleus, 

 albuminous granules, small starch grains, and oil. 



The first division wall cuts off a small cell from one end, 

 which undergoes no further development, and represents the 

 vegetative part of the prothallium, which is here absolutely 

 rudimentary. The rest of the spore forms at once the single 

 antheridium. In the latter two, walls are formed so inclined to 

 each other as to include two upper cells and one lower one (Fig. 

 310, C). This latter next divides into two by a vertical longi- 

 tudinal wall, and each of the resulting cells is further divided 

 by a periclinal wall, so that the antheridium consists of four per- 

 ipheral cells and two central ones. The latter finally divide 

 again, by vertical walls, making four central cells, which become 

 at once the sperm cells. According to Belajeff the walls of the 

 peripheral cells become dissolved finally, so that the sperm cells 

 float free within the spore cavity. Each sperm cell forms a 

 single colled spermatozoid, which is more slender than that of 

 Marattia, but like it is multiciliate. 



In microtome sections of the germinating spores of /. echino- 

 spora, the walls of the peripheral cells were evident after the 

 spermatozoids were completely formed, and there seems some 

 doubt w^hether they are absorbed at all. Occasionally (Fig. 

 310, D) the sperm-cells were divided into two separate groups 

 as in Marsilia. 



The macrospores are very many times larger than the micro- 

 spores, and are of the tetrahedral type instead of bilateral. 

 They are nearly globular in form and show plainly the three 

 converging ridges on the ventral surface. If the fresh spore 

 is crushed in water, its contents appear milky, and microscopic 



