48 THE LOWER FUNGI— PHYCOMYCETES 



into a number of naked protoplasts, each of which tlien assumes 

 a wall and functions as a summer sporangium or resting spore. 



1. Thallus never functioning in its entirety as a single sporan- 



gium or resting spore, but in some cases said to form a soral 

 membrane before breaking up into sporangia; sporangia 

 germinating by a small number (one to eight) of amoeboid 

 or uniciliate zoospores; cilium demonstrated in but few 

 cases, where known attached to the anterior end of the 

 zoospore; vegetative mitosis of a peculiar protomitotic or 

 cruciform type. 



1. Plasmodiophoraceae, p. 48 



2. Mature thallus in some genera forming a membrane and 



functioning as a single sporangium or resting spore, in 

 others fragmenting into a number of naked protoplasts 

 each of which then assumes a membrane; a common soral 

 membrane never formed; sporangia typically multispored; 

 zoospores laterally biciliate. 



2. Woroninaceae, p. 66 



B. Thallus provided from an early period with a thin membrane, 

 clearly discernible within the plasma of the host cell; zoospores 

 uniciliate; cilium attached at the posterior end of the spore. 



1. Thallus at maturity functioning in its entirety as a single 



sporangium or resting spore. 



3. Olpidiaceae, p. 71 



2. Thallus at maturity either developing a thick wall and func- 



tioning as a resting spore, or its protoplast divided by 

 cleavage planes to form a sorus of sporangia enclosed in a 

 common soral membrane. 



4. Synchytriaceae, p. 80 



II. Mycelium present, though usually only slightly developed and of delicate 

 threads of small diameter; thallus intra- or extramatrical. 



A. Mycelium not wide-spreading, usually confined to one or two cells 



of the host, bearing only a single sporangium, and usually in 

 open connection with it at maturity; sporangia usually epibiotic. 



5. Rhizidiaceae, p. 88 



B. Mycelium wide-spreading, developing terminal and intercalary 



enlargements which are transformed wholly or in part into 

 sporangia or resting spores. 



6. Cladochytriaceae, p. 100 



Plasmodiophoraceae 



Inasmuch as the members of this family have long been 

 regarded by many students as parasitic slime moulds their 

 inclusion in the Chytridiales necessitates a more lengthy explana- 

 tion that would otherwise be given. It can best be provided by 



