CHYTRIDIALES 499 



ly pyriform, 10-16 \l high by 12-23 \x in diameter (up to 30 by 35 \l), 

 with a prominent apical solid operculum which, upon discharge of the 

 zoospores, remains attached to the sporangium and often falls back 

 into place, covering the orifice; zoospores spherical, 3-4 \x in diameter, 

 posteriorly uniflagellate, with a colorless globule; rhizoids stout, branch- 

 ing; resting spore spherical, 11-16 jjl in diameter, endobiotic, with a 

 smooth somewhat thickened wall and one or more large oil globules. 



Parasitic on Cymbella sp., Sparrow (loc. cit.), United States; Cym- 

 bellasp., Friedmann (1952: 187), Austria. 



Large sporangia, about 30 [ji high by 35 (j. in diameter, were occasion- 

 ally observed. Other, possibly abnormal, ones, ovoid, pyriform, or 

 irregular in shape, with very thick walls and a hornlike broadly conical 

 operculum, were also found. The fungus was an extremely virulent 

 parasite and destroyed within a few days nearly all the diatoms present 

 in the dish; after being attacked the chloroplasts of the alga rapidly 

 became discolored and desiccated. In immature sporangia the operculum 

 often appeared invaginated. Such a condition has also been observed 

 in Blastocladia and Nowakowskiella and has been discussed by Scherffel 

 (1926a: 226), who unquestionably correctly assigns to it a function in 

 zoospore discharge. 



Chytridium papillatum Sparrow 



Mycologia, 25: 525, text fig. I, 7. 1933 

 (Fig. 31 D, p. 496) 



Sporangium sessile, pyriform to citriform, 10-11 \x high by 7-8 [i in 

 diameter, smooth-walled, with a prominent broad apical papilla sur- 

 mounted by a convex operculum; rhizoidal system short, delicate, 

 sparsely branched, arising from a stouter endobiotic subsporangial 

 stalk; zoospores spherical, about 3-4 \x in diameter, posteriorly uni- 

 flagellate, with a colorless globule; resting spore not observed. 



On filaments of Stigeoclonium sp., United States. 



In the shape of its sporangium and the nature of its rhizoidal system 

 the organism is exactly like Rhizophydium mammillatum (Br.) Fischer. 

 From the accounts of Braun, Sorokin, Dangeard (as Chytridium asym- 

 metricum), and Couch, however, R. mammillatum is inoperculate (see 



