CHYTRIDIALES 71 



The genus Pyrrhosorus Juel (1901: 14) founded on P. marinus 

 Juel, a saprophyte in dead branches of Cystoclonium purpura- 

 scens, is imperfectly known, but seems to fall near Woronina. 



Olpidiaceae 



Mycelium wholly lacking; thallus intramatrical, provided from 

 an early period with a thin membrane, at maturity functioning 

 in its entirety as a single sporangium or resting spore; zoospores 

 uniciliate; cilium at the posterior end of the spore. 



Key to Genera of Olpidiaceae 



I. Sporangium lying free in the host cell. 



A. Sporangium not provided with numerous exit tubes. 



1. Mature sporangium ellipsoidal to fusiform, lacking elongate 



exit tubes, dehiscing at one or both ends by a simple pore 

 or short papilla. 



1. Sphaerita, p. 72 



2. Mature sporangium more or less globose. 



a. Resting spore globose to ellipsoidal, becoming stellate 

 by shrinkage; sporangium sometimes dehiscing by a 

 simple pore, sometimes by an exit tube. 



2. Olpidiaster, p. 72 



h. Resting spore not becoming stellate by shrinkage; 

 sporangium dehiscing by one to few elongate exit 

 tubes. 



(1) Resting spore not bearing a companion cell. 



3. Olpidium, p. 73 



(2) Resting spore bearing one or more companion cells. 



4. Pseudolpidiopsis, p. 76 



B. Sporangium with numerous exit tubes. 



1. Sporangium tubular; exit tubes short and arranged in a row. 



5. Ectrogella, p. 77 



2. Sporangium globose; exit tubes long and protruding in many 



directions. 



6. Pleotrachelus, p. 78 



II. Sporangial wall tightly appressed to the wall of the host cell. 



A. Wall of host and that of parasite completely fused; no line of 



demarcation discernible between them; parasites on other fungi. 



7. Pleolpidium, p. 78 



B. Walls of host and parasite merely in contact, not fused; parasites 



in algae. 



8. Plasmophagus, p. 70 



