OOMYCETES 



71 



reminiscent of the Achlya type; the zoospore initials pass out through an 

 emission collar, collect before its opening in the form of a hollow sphere 

 and surround themselves with a membrane. After a short time they 

 slip out and, leaving behind the empty sheath, swarm away as reniform, 

 laterally flagellate zoospores. Occasionally they do not shed the mem- 

 brane so that the zoospores of the second swarm stage arise directly in the 

 sporangium. Sexual organs have not yet been determined with certainty. 



Fig. 42. — Araiospora spinosa. Plant with simple and echinate sporangia. (After Minden, 



1916.) 



In Rhiphidium and Araiospora both of which (like Apodachlya) possess 

 laterally flagellate zoospores, the main axis is shortened and becomes a 

 voluminous broad cylinder which bears a tuft of auxiliary axes. These 

 axes may terminate in a sporangium or branch terminally like the main 

 axis. 



The species of Rhiphidium, as R. europaeum, live on rotting fruits 

 and fallen twigs in water. Their mycelium is reminiscent of allo- 

 myces (Fig. 35, 2); it consists of a very large thick-walled basal cell 



