CHYTRIDIALES 407 



by 4 \l in diameter, with a spherical companion cell 3 \i in diameter; 

 germination not observed. 



Parasitic on Protoderma sp., coll. E. F. Warburg, North Africa 

 (Tangier). 



RHIZIDIUM Braun 



Monatsber. Berlin Akad., 1856: 591; Flora, 14: 599. 1856 

 (Figs. 11 J, p. 110; 25 E-G, I-J, p. 411; 28 E-G, p. 440) 



Thallus monocentric, eucarpic, consisting of a sporangial rudiment 

 (the body of the encysted zoospore) and a broad main rhizoidal axis 

 which bears secondary branches; zoosporangium inoperculate, formed 

 from the sporangial rudiment ; zoospores posteriorly uniflagellate, with 

 a single globule, usually emerging imbedded in slime or surrounded by 

 a vesicle through one or more pores, forming a motionless mass at the 

 orifice, eventually separating and either swimming directly away or 

 undergoing a period of collective swarming in a vesicle before escaping; 

 resting spore thick-walled, borne like the sporangium on the thallus, 

 asexually or sexually formed, upon germination functioning as a 

 prosporangium. 



On the cells and gelatinous sheaths of algae, in insect exuviae and 

 vegetable debris. 



The lack of figures in Braun's original account of the genus and the 

 vagueness of his description have resulted in a variety of interpretations 

 of Rhizidium. The confusion has largely centered around what was 

 meant by the "two-celledness" (of the plant) which, together with "a 

 prolonged main rhizoidal axis," was emphasized by Braun as charac- 

 teristic of R. mycophilum, the type species. The accepted understanding 

 of the type is that elaborated by Nowakowski (1876a: 87; 1876b: 215); 

 see, however, page 410. The genus was understood by Fischer (1892: 106) 

 to include the Rhizophydium-Rko forms with subsporangial apophyses 

 now placed in Phlyctochytrium. Dangeard (1889b) interpreted Rhizidium 

 similarly but assigned to it operculate as well as inoperculate species. 

 Zopf (1884) evidently included in it all monocentric inoperculate 

 chytrids with tapering rhizoids. Schroeter (1885: 193; 1893: 79)correctly 

 interpreted the genus and re-established Rhizidium in its original sense. 



