CHYTRIDIALES 247 



Rhizophydium pythii de Wildeman 

 Ann. Soc. Beige Micro. (Mem.), 21: 12, pi. 1, figs. 10-17. 1897 



Sporangium sessile, spherical, with one short papilla (occasionally 

 two), of varying size, wall smooth, colorless; rhizoids very delicate, 

 branched, arising from a short main axis; zoospores spherical, with 

 a small centric globule and a long flagellum, escaping through pores 

 formed upon the dissolution of the papillae; resting spore not observed. 



Parasitic on the oospores (and sporangia?) of Pythium monospermum 

 {complens), France. 



Although the sporangia are said to be spherical, the figures show 

 such wide variations that it is difficult to decide just what shape is to 

 be considered typical. Rhizophydium pythii was thought by de Wilde- 

 man to perhaps be only a form of R. globosum. 



The fungus is said in the text of the original description to parasitize 

 the oospores, whereas in the formal diagnosis it is said to be "sur les 

 zoosporanges." 



Rhizophydium mycetophagum Karling 

 Amer. J. Bot., 33: 329, figs. 17-18. 1946 



"Thalli numerous, up to 25 on a host cell. Sporangia sessile, hyaline, 

 smooth, spherical (7-20 \i), broadly pyriform (8-12 x ll-19u.), with 

 one to three exit papillae. Zoospores spherical (3.5-5 u,), with a conspic- 

 uous (1-1.5 (jl) refractive globule. Rhizoidal system relatively delicate 

 but richly branched. Resting spores spherical (6—14 p.) with a thick, 

 dark brown rough wall, and one to several large refractive globules; 

 germination unknown" (Karling, loc. cit.). 



Parasitic on the conidiophores and hyphae of the mucor Choancph- 

 ora sp., Brazil. 



The species appeared limited in its host range and did not attack 

 other chytrids, Oomycetes, pollen grains, or algae. No other mucors 

 were available at the time for cross-inoculation experiments. This and 

 the species Pleotrachelus fulgens and P. zopfianus are the only known 

 chytrid parasites of mucors. 



