SAPROLEGNIALES 



165 



7. Pythiopsis de Bary (1888: 632). 



The type species, P. cymosa de Bary (Fig. 59), has been studied 

 in North America by Humphrey (1893: 113) and Coker (1923: 

 18). Two other species, P. humphreyana Coker (1914: 292) 

 and P. intermedia Coker & Harvey (Harvey 1925: 157) have 

 been added to the genus in recent years. The sporangia of P. 

 cymosa are ovoid and recall those of Pythium, but in the other 

 species great variation occurs, the sporangium sometimes being 

 leongate as in Ac.hlya. The swarmspores as they emerge from the 



Fig. 59.^ — Pythiopsis cymosa de Bary. (a) Cymose development of swarm- 

 sporangia, (b) Oogonium accompanied by antheridia. (c) Mature oospore. 

 (After de Bary 1888.) 



sporangium in this genus are pyriform and terminally biciliate. 

 While monoplanetic as regards form they apparently have been 

 observed to swim twice in P. intermedia, thus recalling the 

 phenomenon of repeated zoospore emergence described in Dicty- 

 iichus by Weston. 



The genus differs from Pijthium in the form of the swarmspore, 

 which is reniform and laterally biciliate in that genus, in the fact 

 that the oogonia though typically monosporic sometimes contain 

 two or more oospores, in the much broader hyphae, and in the 

 manner of sporangial germination. 



