498 AQUATIC PHYCOMYCETES 



zoospores spherical, 2.5-5 jx in diameter, with a colorless centric globule 

 and a fairly long flagellum, escaping fully formed after the dehiscence 

 of the operculum; resting spore not observed. 



On Zygnema sp., Dangeard (be. cit.), France; Spirogyra sp., Stig- 

 eoclonium sp., Sparrow (1933a: 64, fig. 1 g-i), United States; Spirogyra 

 sp., Mougeotia sp., Achlya (?), Sparrow (1936a, fig. 3a-f), Great 

 Britain; ? Cladophora sp; Berczi (1940: 84, fig. 27-29), Hungary. 



Dangeard identified his fungus with Rhizidium sphaerocarpum Zopf 

 (Rhizophydiumsphaerocarpum[Zopf] Fischer), butplaced it in Chytridium 

 because of the lack of a basal cell (a feature of Rhizidium in the sense 

 of Fischer) rather than because of the presence of an operculum. 



The species is a difficult one to characterize, but its principal features 

 are a narrowly pyriform sporangium, often appearing tilted (asym- 

 metrical), an extremely delicate operculum, and a long rhizoid which 

 sometimes forms a few branches at its tip. The chytrid on Mougeotia 

 does not conform in this last detail, since the rhizoids branch near the 

 host wall. Perhaps it should not be included here. Morphologically, the 

 fungi found on Spirogyra and Stigeoclonium are indistinguishable from 

 the fungus on Achlya. 



Chytridium oocystidis Huber-Pestalozzi 

 Zeitschrift f. Hydrologie, 10 (1): 120, figs. 1-8. 1944 



Sporangia sessile on the gelatinous sheath of the host colony, ovate 

 to pyriform with a broad blunt apex, gregarious, rarely solitary, with 

 a smooth, colorless wall, 13-14.5 u. long by 5.5-7.8 jx wide; rhizoidal 

 system consisting of a single tenuous, unbranched rhizoid; zoospores 

 spherical, with one oil droplet, discharged after the dehiscence of an 

 operculum; resting spore not observed. 



Parasitic on the planktonic alga, Oocystis lacustris, Switzerland. 



Doubtfully distinct from Chytridium sphaerocarpum. 



Chytridium perniciosum Sparrow 



Mycologia, 25: 526, pi. 49, figs. 9-11. 1933 



(Fig. 31 C, p. 496) 



Sporangium sessile, smooth-walled, spherical at first, becoming broad- 



