CHYTRIDIINEAE 63 



A careful study of the nuclear processes of these alleged 

 plasmodium-forming genera is greatly to be desired. 



Sorus-formation. It is shown in Fig. 16 how a single 

 zoospore of Olpidiopsis without loss of individuality developes 

 into a single sporangium ; in an allied genus, Pseudolpidium, 

 either a single sporange or, as an alternative, a group of 

 sporanges or sorus may be produced. Sorus-formation is 

 the rule in Woronina. 



Course of the Disease. The effects of infection by the 

 olpidians on their hosts constitute a disease, and the remarks 

 of E. J. Butler are of importance : " Cases were observed 

 in which the presence of the parasite did not interfere with 

 the normal life of the host, even to the extent that normal 

 sporangia and zoospores were formed, and it was only later 

 on when secondary sporangia were forming, that the parasite 

 gained the upper hand. . . . The zoospores of the parasite 

 often infected Saprolegnia zoospores during their first 

 encystment without checking the process of diplanetary 

 formation of secondary zoospores, though whether the 

 latter developed into a mycelium was not ascertained." 



With the aid of a pocket-lens Cornu was able to separate 

 Saprolegnia-filaments in which were older parasites, but 

 the microscope was required to detect their earlier stages. 

 When the parasites first become visible under the micro- 

 scope they look like condensed portions of the host's plasm, 

 Fig. 15, A ; a little later they become more definite, B ; 

 later still, as at (7, they are large, well-defined, and some 



