CHYTRIDIALES 129 



Olpidium apiculatum (Entoph/yctis), O. endogenum, and O. saprolegniae 

 (Olpidiopsis). Rabenhorst emphasized the inoperculate sporangium 

 and the presence of a discharge tube as characters common to all 

 the species regardless of their relation to the substratum. Hence Rhi- 

 zophvdiwn ampullaceum even though epibiotic fell within these limits 

 and was included in the genus. Schroeter (1885: 180) established Ol- 

 pidium as it is here understood and it has so been maintained by sub- 

 sequent monographers, that is, as a genus confined to endobiotic ho- 

 locarpic chytrids without rhizoids and with one, or occasionally several, 

 discharge tubes. His assertion that the zoospore was anteriorly flagel- 

 late is incorrect, however, and probably rests on Fisch's observations 

 on "O. lemnae" (now IReessia lemnae, see p. 765). Because of this 

 character in Schroeter's description of the genus Lagerheim (be. cit.) 

 was led to establish Olpidiella for forms with posteriorly uniflagellate 

 zoospores. 



Endolpidium hormisciae de Wildeman (1894) in Hormiscia zonata 

 in France differs from species of Olpidium only in forming a short 

 discharge tube which does not penetrate the algal wall and in producing 

 hypertrophy of the host wall. The zoospores and resting spores were 

 not observed. 



Cyphidium was established by Magnus (loc. cit.) as a subgenus of 

 Chytridium for O/pidium-like forms in which the sporangium rests 

 between the wall and the protoplasm of the host. No combinations, 

 however, were made. (See remarks under O. zygnemicola, p. 134). 

 Petersen (1910: 504, footnote) applied the generic name Oligostomum 

 to "Olpidium-shapGd marine forms with uniftagellated zoospores and 

 with a limited number of channels for the zoospores (several Pleotra- 

 chelus forms)." 1 His description is too inadequate and too vague to be 

 tenable, and no species is named which would typify the genus. Astero- 

 cystis de Wildeman (1893a: 21), erected for an Olpidium-tike parasite 

 in the roots of terrestrial flowering plants, has been discussed by Kar- 

 ling (1937d). 



A genus Gamolpidium (G. nitidis) is mentioned by Constantineanu 

 (1901) as having been established by Vladescu (1892). 



Sexuality has been demonstrated to occur in several species of 

 Olpidium parasitic in certain flowering plants (Kusano, 1912, 1929), 



