CHYTRIDIALES 363 



uously expanded at the point of origin of the primary branches; 

 zoospores spherical (?), 3-4 \x in diameter, with a globule, escaping 

 through a broad apical pore 9-10 \x in diameter; resting spore not 

 observed. 



Parasitic in, and causing an epidemic of, the planktonic diatom 

 Stephanodiscus niagarae, United States. 



An exceedingly high percentage of the diatom population was in- 

 fected by the chytrid. Although as many as fifty to sixty or more thalli 

 were sometimes present on one diatom, a single infection could result 

 in total destruction of the host. 



Podochytrium emmanuelense (Sparrow) Sparrow and Paterson 



Mycologia, 47: 274. 1955 



(Fig. 21 B-E, p. 360) 



Rhizidiopsis emmanuelensis Sparrow, Trans. Brit. Mycol. Soc, 18:216. 

 1933; J. Linnean Soc. London (Bot.), 50: 451, pi. 18, figs. 1-13. 1936. 



Sporangium smooth-walled, obpyriform or clavate, 6-26 \x long by 

 5-13.5 u. in diameter, the long axis often parallel with that of the host 

 filament, sessile, or on a short pedicel, attached by its narrower end to 

 the rounded cyst, 3-4 \x in diameter, of the zoospore with which it is 

 either continuous or more often cut off by a cross wall, forming from 

 four to twelve or more zoospores, 3-4 \x in diameter, which at maturity 

 are discharged through a single apical pore ; endobiotic system composed 

 of branched broad coarse straplike elements, 1-2 u. in diameter, with 

 relatively blunt apices; resting spore spherical or somewhat flattened, 

 thick-walled, 4-4.5 [x in diameter, surrounded by a dark-brown rough 

 incrustation, upon germination producing a sporangium. 



Parasitic on Melosira varians and Nitzschia (?) sp., Sparrow (1936a: 

 451), Melosira sp., Ingold (1941, coram.), Great Britain; Pinnularia 

 viridis, Pinmdaria sp., Melosira varians, Melosira sp., Amphora ovalis, 

 Gomphonema macropus, Tabellaria flocculosa, Friedmann (1952: 192, 

 fig. 3), Austria; Melosira sp., Sparrow and Paterson (1955), United 



States. 



The fungus that Friedmann described as Podochytrium clavatum is 

 placed in P. emmanuelense by reason of its coarse, straplike rhizoidal 

 system. 



