580 AQUATIC PHYCOMYCETES 



MEGACHYTRIACEAE 



Thallus epi- and endobiotic, or free in the medium, only the tips 

 entering the substratum, polycentric, either rhizoidal, extensive, and 

 much branched, with intercalary swellings, or broadly tubular, hypha- 

 like, not distinctly rhizoidal, with swellings or constrictions and some- 

 times septae; zoosporangia operculate, formed from terminal or inter- 

 calary swellings; zoospores posteriorly uniflagellate; resting spores 

 thick-walled, apparently asexually formed, upon germination producing 

 zoospores or functioning as a prosporangium. 



Saprophytes in vegetable debris, members of one genus (Megachy- 

 trium) saprophytic and possibly parasitic on Elodea. 



This family includes all polycentric operculate chytrids except those 

 in Tetrachytrium and Zygochytrium. These genera are placed at the end 

 of this family, although not belonging in it (see pp. 599-601). When 

 further observations validate the two (particularly Tetrachytrium), each 

 should, perhaps, be put in a family of its own, since they possess 

 radically different types of sexual reproduction (see "Sexual Reproduc- 

 tion," p. 79). 



KEY TO THE GENERA OF THE MEGACHYTRIACEAE 



Thallus forming tenuous strongly tapering rhizoids 



Rhizoids septate only where delimiting the reproductive organs 



NOWAKOWSKIELLA, p. 580 



Rhizoids septate and constricted at intervals as well as where 



delimiting the reproductive organs Septochytrium, p. 592 



Thallus forming a broadly tubular vegetative system not tapering 



strongly distally Megachytrium, p. 596 



NOWAKOWSKIELLA Schroeter 



Engler and Prantl, Natiirlichen Pflanzenfam., 1 (1): 82. 1892 (1893) 



(Fig. 35, p. 583) 



Cladochytrium Nowakowski, pro parte, in Cohn, Beitr. Biol. Pflanzen, 

 2: 92. 1876. 



Thallus eucarpic, polycentric, endobiotic, extramatrical, or both, 

 extensive, branched, rhizoidal, bearing irregular swellings, occasionally 

 septate turbinate cells, and the rudiments of the zoosporangia and 



