CHYTRIDIALES 489 



rhizoid or with a subsporangial apophysis has never been made, as it 

 has among the inoperculate species. 



Scherffel (1925b: 7) suggested that Zygorhizidium willei, with Chy- 

 tridium-tike operculate sporangia and epibiotic resting spores, be in- 

 cluded in a new subgenus of Chytridium, Ectochytridium. In view of the 

 type of sexuality which occurs in Zygorhizidium Lowenthal (see p. 547) 

 it would appear better to retain his genus as distinct. Furthermore, 

 Karling (1945c) has erected a genus, Chytriomyces, whose characters 

 are essentially those of Scherffel's subgenus Ectochytridium. Fisch 

 (1884b) described copulation of motile bodies preceding the formation 

 of endobiotic resting spores in "Chytridium mesocarpi" Fisch, p. 766. 

 The correctness of his account has been questioned by both Fischer 

 and Minden, neither of whom, however, noted that Fisch's fungus 

 produced anteriorly uniflagellate zoospores and, hence, was no Chytrid- 

 ium (see Hyphochytriales, p. 743). 



The only authentic detailed account of the sexual process in a member 

 of this genus is that by Koch (1951). He reports that in Chytridium 

 sexuale a zoospore comes to rest on the host cell and undergoes develop- 

 ment similar to that of the sporangium. At an early stage in the for- 

 mation of this female thallus a free-swimming spore attaches itself to the 

 distal part, encysts, and penetrates by means of a tube. The contents 

 of the male then pass through the tube and the combined protoplasts 

 migrate into the endobiotic apophysis, which becomes converted into 

 a thick-walled resting spore. As Koch mentions, such behavior also 

 occurs in the zoospores of another apophysate species, C. lagenaria 

 (Sparrow, 1936a), when it grows under conditions of poor nutrition. 

 In the latter instance, however, revitalized growth of the receptive 

 thallus rather than a resting spore resulted. 



The curious expansion of only a portion of the cyst in the infecting 

 zoospore of Chytridium schenkii and related species was first noted by 

 Schenk (1858b). 



In view of Karling's (1948b) statements indicating that he considers 

 nonapophysate species of Chytridium belong elsewhere, it should be 

 emphasized that Braun's material of C. olla, the type species, was 

 without an apophysis and so, too, was American material collected 

 by Sparrow (compare C. brevipes Braun). 



