LAGENIDIALES 915 



the zoospore segments are delimited endogenously, they emerge and 

 encyst at once at the tube orifice, later giving rise (from the cysts) to 

 flagellated zoospores. Finally, in L. distylae they are entirely delimited 

 and matured outside the sporangium within a vesicle, as in L. raben- 

 horstii and in Pythium. Still another example of variation might be 

 cited. In L. destruens Sparrow (1950) zoospores are matured as in L. 

 distylae but no vesicle is formed. 



The functional zoospore in both Myzocytium and Lagenidium is of 

 the secondary, beanlike, kidney-like, or grape-seed-like, type, with a 

 shallow sinus from which arise two oppositely directed flagella of 

 approximately equal length. The contents frequently bear numerous 

 refractive granules and a centrally disposed vacuole. The movement is 

 an even gliding, sometimes accompanied by a gentle lateral rocking of 

 the whole body. Couch (1935b) noted in an unnamed species of Lagen- 

 idium occurring in Oedogonium, as did Karling (1944g) in L. distylae, 

 that the zoospores after coming to rest and encysting may emerge from 

 the cysts again as secondary zoospores and undergo a second swarm 

 period (''repeated emergence"), a further point in which these fungi 

 resemble Pythium. 



Dangeard (1903b) gave an account of the cytology of the thallus and 

 of zoospore formation in Myzocytium vermicola, a parasite of nema- 

 todes. The young thallus contains numerous nuclei dispersed in a 

 reticulate cytoplasm. After formation of the cross walls the number of 

 nuclei is augmented, but no division figures were observed. As the 

 sporangia thus delimited approach maturity, the cytoplasm and nuclei 

 become disposed around a large central vacuole, formed probably by 

 the coalescence of several smaller ones, which were previously visible. 

 Lines of granules then delimit irregular polyhedral areas. The central 

 vacuole disappears and the protoplasm fragments into uninucleate 

 zoospores which are discharged through a tube to the outside. 



Sexual Reproduction 



Sexual reproduction is known in the Olpidiopsidaceae and the 

 Lagenidiaceae. No well-authenticated occurrence of resting spores of 

 either sexual or asexual origin has been reported in the Sirolpidiaceae. 



