CHYTRIDIALES 567 



dal axis by a concave cross wall; rhizoidal axis stout, 400-450 u, long by 

 60-90 [j. in diameter, divided basally into a rootlike complex of coarse 

 wide-lumened thick-walled richly branched rhizoids which are imbedded 

 in the substratum; zoospores up to a thousand in large sporangia, spher- 

 ical, with a long flagellum, emerging through a broad apical pore formed 

 upon the dehiscence of a broad convex smooth operculum that occasion- 

 ally bears at the center of its inner wall a short peglike outgrowth, the 

 emerged spores surrounded by a delicate vesicle which ruptures when 

 about one half the size of the sporangium, movement of zoospores at 

 first amoeboid, later, when free of the surrounding bacterial mass, swim- 

 ming; resting spore (?) borne like the sporangium, contents with glob- 

 ules, germination not observed. 



Saprophytic on rotting fruits, especially apples, possibly also on old 

 submerged twigs, Minden (loc. cit.), Germany; twigs of various trees 

 (Quercus, Abies, Fraxinus, Alnus, Aesculus), Lund (1934: 56. fig. 29), 

 Denmark; submerged pears, coll. B. B. Kanouse, in Sparrow (1943: 

 368), United States. 



Lund noted that his fungus, which was 100-558 \x long, was usually 

 collected in pools of stagnant water where there was much decaying 

 vegetable material and where the surface was frequently covered by 

 aquatic angiosperms. It occurred in tufts on the twigs in company with 

 Blastocladia, Rhipidium, and the like, always covered by bacteria. From 

 these facts he concluded that it did not require much oxygen for its 

 existence. Kanouse frequently found it in the vicinity of Ann Arbor, 

 Michigan, on submerged pears. Macrochytrium is the largest of the 

 monocentric chytrids. 



The fungus studied physiologically by Crasemann (1954) has been 

 identified in our laboratories as probably a species of Cylindrochy Irid- 

 ium and not a Macrochytrium. 



SUBFAM. ENDOCHYTRIOIDEAE 



Sporangium, rhizoids, and resting spore endobiotic; epibiotic part 

 an evanescent or persistent cyst. 



