BLASTOCLADIALES 625 



other genera of the Blastocladiales. For example, the Cystogenes type 1 

 is present in Catenaria (C. allomycis) (Fig. 44 B-F, p. 651) and all three 

 occur in Blastocladiella. For this reason use is here made of Euallomyces, 

 and the other terms, in keys and elsewhere, even when such application 

 precedes the treatment of the genus Allomyces itself. 



In the Cystogenes life cycle (Fig. 43, p. 629) characteristic of Allo- 

 myces moniliformis, A. cystogenus, and A. neo-moniliformis, the zoospores 

 from the resting spore are large, sluggish, and usually posteriorly bi- 

 flagellate. According to McCranie (1942) and Teter (1944), in some, 

 flagella are present, in others they are apparently lacking. Teter assumed 

 two flagella to be normal. Wilson's (1952) cytological study confirmed 

 both Teter's observations and his own contention that the number of 

 flagella present will conform to that of the number of nuclei in the spore. 

 The zoospores encyst at once and from each, four small gametes emerge 

 which may or may not have a flagellum. These gametes fuse in pairs 

 to form a zygote which gives rise to the sporophyte plant. 



Wilson (1952) not only clarified certain of McCranie's (1942; also 

 in Sparrow, 1943) observations but the homologies between the Cys- 

 togenes and Euallomyces life cycles as well. There are approximately 

 the same number of nuclei in resting spores of both. In Cystogenes and 

 Euallomyces the two meiotic divisions occur in the germinating resting 

 spore. In the former, before cleavage of the cytoplasm into resting-spore 

 zoospores ("meiospores") its nuclei pair, members of each pair being 

 held together by a common nuclear cap. At cleavage binucleate spores 

 are formed; these emerge, each with two flagella, and encyst. During 

 encystment the only haploid mitotic division in the life cycle takes 

 place and by it the nuclei in the cyst are increased to four. Individual 

 nuclear caps are now formed and four gametes are produced in each 

 cyst. The cyst in Cystogenes is considered homologous with the game- 

 tophyte plant in Euallomyces. Wilson thinks it probable that in the Cys- 

 togenes group the cyst is homothallic as is the gametophyte of Euallo- 

 myces. He also infers from the pairing of nuclei in the resting spore 

 that the gametes in the cyst are at least physiologically differentiated 

 as to sex. 



In the Brachyallomyces life cycle neither sexual plants nor cysts are 



1 In all likelihood it occurs in some species of the chytrid genus Micromyces (p. 1 92). 



