76 AQUATIC PHYCOMYCETES 



apart to opposite sides of the ceil, which is now surrounded by a thick 

 spiny wall. Considerable chromatin is extruded from the nuclei, and 

 as a result they become smaller and show less affinity for stains. The 

 extruded, deep-staining material eventually becomes massed in the 

 center of the cell. At the time of germination the resting spore functions 

 as a prosporangium. There is protruded from its ruptured wall a sphere 

 which increases in size as the contents of the spore emerge into it. 

 The two nuclei pass out into the sporangium (Fig. 5 I) and there fuse 

 (Fig. 5 J). The fusion nucleus then multiplies to form the nuclei of the 

 zoospores, which are eventually cleaved out from the contents. Al- 

 though meiosis was not observed it has been supposed to occur at the 

 first division of the fusion nucleus in the sporangium formed by the 

 resting spore (Fig. 5 K). On this hypothesis and proceeding from the 

 fact that in Nowakowski's cultures nearly equal numbers of male 

 and female thalli were formed, Kniep (1928) has proposed that the 

 fungus is dioecious and that the zoospores are sexually differentiated. 

 He suggests {op. cit.) the following developmental cycle: 



zoosporangium — $ plant — zoosporangium. . . . 

 / 9 zoospore — $ plant 



$ plant 



/ 9 zoospore — $ plant 



zygote — germ sporangium R.D. 



£ zoospore — $ plant 



<$ plant 



^zoospore — $ plant 



zoosporangium — <$ plant — zoosporangium. . . . 



Bartsch (1945) noted that in Polyphagias laevis the zygote was always 

 formed terminally in the conjugation tube and, hence, at maturity 

 was directly adnate to the female thallus (Fig. 4 Z'). 



In the closely related Sporophlyctis rostrata, fusion of two uninucleate 

 thalli of equal size takes place (Serbinow, 1907) (Fig. 4 X, p. 72). 

 One thallus receives the contents of the other through a pore. The 

 distal part of the receptive thallus is then transformed into a thick- 



