KEY TO THE MORE IMPORTANT FAMILIES AND GENERA 73 



Zoosporangium spherical or ellipsoidal. 



Rhizoids delicate. Rhizodosmatium 



Rhizoids coarse." Siphonaria 



Exit tube operculate near base, interbiotic. Karlingia 



Exit tube operculate at apex, epibiotic. Chytridium 



Zoospore cyst enlarging into a prosporangium. 



Epibiotic, operculate, small, rhizoids not massive. Chytridium 



Epibiotic, operculate, rhizoidal system massive. Macrochytrium 



Interbiotic, inoperculate. Polyphagus 



Zoospore cyst not enlarging into zoosporangium or prosporangium, but upper 

 part of germ tube so enlarging. 



Family Entophlyctaceae 

 Exit tube or papilla inoperculate. Endobiotic. 



Upper part of germ tube becoming a zoosporangium. Entophlydis 

 Zoosporangia arising by enlargement of the proximal portions of the 



rhizoidal branches. Phlyctorhiza 



Upper part of germ tube becoming a prosporangium. Diplophlyctis 

 Exit tube operculate, germ tube enlarging into a zoosporangium. 

 Epibiotic. Rhizoids constricted into catenulate segments. 



Catenochytrium 

 Endobiotic. Rhizoids not constricted. Endochytrium 



Exit tube operculate. Endobiotic. Germ tube enlarging into a prosporangium. 

 Eucarpic and polycentric. 



Nephrochytrium 



Mostly saprophytic, intra- and extramatrical, with many centers connected 



by slender (rarely stout) tubes. Sporangia thin-walled, 



terminal and often intercalary. Resting spores thick-walled, 



apparently not sexually produced. 



Family Cladochytriaceae 

 Sporangial openings inoperculate. 



Rhizomycelium slender, branching, intramatrical, with turbinate cells. 

 Zoosporangia intercalary and terminal. Resting spores thick- 

 walled, acting as prosporangia when germinating. 



Cladodiytrium 

 Rhizomycelium slender, branching, mostly extramatrical, rarely with 

 turbinate cells. Zoosporangia and resting spores single at the 

 apex of hyphae or branches. On pine pollen in water. 



Physodadia 

 Rhizomycelium coarse, branched, without turbinate cells or intercalary 

 swellings. Zoosporangia usually in clusters of two or more 

 at tips of hyphae or intercalary. No resting spores although 

 thicker-walled, tuberculate zoosporangia are formed which 

 set free their zoospores promptly. Polychytrium 



Sporangia operculate at the mouth of the opening. 



Intra- and extramatrical rhizomycelium slender and branched, with 

 various more or less fusoid swellings. Zoosporangia formed 

 mostly on the extramatrical rhizomycelium, terminal or 

 intercalary, apophysate. Thicker-walled resting spores some- 

 times formed from a mass of parenchyma-like cells. Zoospo- 

 rangia sometimes proliferating. Nowakowskiella 

 Mainly intramatrical, rhizomycelium moderately stout, constricted occa- 

 sionally and septate or partially so at the constrictions. 



