CHYTRIDIALES 425 



to error. Both Petersen and Sparrow noted sporangia of two size classes. 

 This suggests the possibility that sexual differentiation of zoospores 

 may be present (see discussion under the genus). None was noted 

 by Karling (1945d) in S. petersenii and S. sparrowii. 



Siphonaria sparrowii Karling 



Amer. J. Bot., 32: 581, figs. 27-53. 1945 



(Fig. 26 E-F, p. 422) 



"Thalli numerous, occurring inside insect exuviae. Sporangia extra- 

 matrical to substratum, nonapophysate, hyaline, smooth, spherical, 

 8-20 \x, or broadly pyriform with a low apical or subapical exit papilla. 

 Zoospores spherical, 5.5-6 u,, with a large (3-3.5 jx) hyaline refractive 

 globule; swarming in a vesicle outside the sporangium for several 

 minutes before breaking out and swimming away. Rhizoidal system 

 monoaxial, intramatrical, arising from base of sporangium, rhizoids 

 thick-walled, coarse, tapering abruptly, and often branching at right 

 or obtuse angles. Resting spores oval, spherical, 10-18 \l, with a thick 

 (3-4 [l) amber to dark brown smooth wall; several spores frequently 

 enveloped by a common thick wall; formed sexually by fusion of the 

 content of one or more 'male' thalli with one 'female' thallus; func- 

 tioning as prosporangia in germination" (Karling, be. cit.). 



Saprophytic in exuviae of mayflies, Brazil; United States. 



Differing from Siphonaria variabilis in having the zoospores larger 

 with a colorless droplet, an apical discharge pore on the sporangium, 

 and a distinct vesicle around them when emerged. The resting spores 

 resemble somewhat those of S. variabilis. In some instances the con- 

 jugating thalli may be almost adnate. 



Siphonaria petersenii Karling 



Amer. J. Bot., 32: 580, figs. 1-26. 1945 



(Fig. 26 C-D, p. 422) 



"Thalli numerous, occurring inside of empty insect exuviae. Sporan- 

 gia extramatrical to substratum, non-apophysate, orange-golden in 

 color, predominantly elongately pyriform, 5-20 X 10-36 y., occasionally 

 elongated transversely to rhizoid axis, with a long sharp apical and 



