122 PHYCOMYCETEAE 



Sporangia abundant, the spores emerging from an apical mouth before encyst- 

 ing. 

 Zoospores of primary type only, after escaping from sporangium germinating 

 by germ tube or by repetition forming zoospores again of the pri- 

 mary type. Pythiopsis 

 Zoospores of primary type swimming some distance before encysting, then 

 emerging as secondary type zoospores. 

 Zoospores in a single row in the zoosporangium. Leptolegnia 

 Zoospores in more than one row. 



New sporangia formed by proliferation. Saprolegnia 



New sporangia formed by cymose branching. Isoachlya 



Zoospores of primary type with or without flagella and encysting at the 

 mouth of the zoosporangium, later emerging as secondary type 

 zoospores. 

 Zoospores in more than one row in the sporangium. 



Zoospores all encysting at the mouth of the zoosporangium. New spo- 

 rangia formed by cymose branching. Achlya 

 Zoospores encysting in part at the mouth of the sporangium and some 

 swimming away before encysting. New sporangia formed by cymose 

 branching and sometimes also by proliferation. Protoachlya 

 Zoospores in one row in the slender zoosporangium. 



Masses of lobulate inflated segments auxiliary to the zoosporangia are 



produced. Plectospira 



No lobulate auxihary masses. 



Branches of mycelium of usual type. Aphanomyces 



Spike-like'^^branches' with sticky tips which catch and parasitize 

 rotifers. Sommerstorfia 



Key to the Genera of Family Leptomitaceae 



(Based upon Sparrow, 1943) 



Thallus coarse, branched, constricted into numerous cjdindrical segments. Be- 

 ginning at the apex the segments become zoosporangia in basipetal succession 

 without change of size or shape. No sexual reproduction known. Growing 

 saprophytically, in heavily polluted water. Leptomitus 



Thallus more slender, constricted, the zoosporangia with definite pedicels and 

 mostly ovoid or pyriform. Usually producing sex organs. 

 Oogones with one oospore. Apodachlya 



Oogones with more than one oospore; zoosporangia not reported. 



Apodachlyella 

 Key to the Genera of Family Rhipidiaceae 



Basal cells giving rise to branches which bear the reproductive organs. 



Basal cells slender, sporangia smooth walled, oospores with undulate outer wall. 



Sapromyces 

 Basal cells usually stout, sporangia smooth walled or spiny or both in the 

 same species. Oospores with reticulate or cellular outer wall. 

 Oospore wall cellular, both smooth and spiny sporangia present. 



Araiospora 

 Oospore wall reticulate, sporangia with smooth walls. Rhipidium 



Reproductive organs arising directly from the basal cell and of varying degrees 

 of spininess. Mindeniella 



