34 PKOTISTS AND DISEASE 



Parasites of Saprolegnia. Chytridian parasites such as 

 Woronina and Eozdla often occur in cultures of different 

 species of Saprolegnia. It is Eozella that causes the curious 

 septate condition shown in Fig. 3, D and E. The number 

 of compartments found in any one filament varies ; it 

 depends on the number of parasites that penetrate : the 

 more the parasites the more the compartments, though not 

 in strict numerical proportion because fusion of parasites 

 occurs. Each compartment is a sporangium of the parasite, 

 its wall adherent to the cell- wall of its host. The zoospores 

 of the Chytridian are evacuated in from 60 to 90 hours after 

 infection through a hole at the side, Fig. 3 ; E, o, o. Resting 

 spores are also formed: lateral shoots are protruded and 

 typical chytridian resting spores are formed, causing a 

 curious resemblance to the hosts' ovum in the ovary, as in 

 Fig. 3; E, rs ; but Cornu noticed that the protrusion 

 containing the parasite is not shut off by a septum as the 

 ovary is. 



Peronosporeae. The next group of the Phycomycetes 

 is called the Peronosporeae, and includes the genera Pythium, 

 Peronospora, Phytophthora, and Cystopus. 



Pythium. The genus Pythium was founded in 1858 

 by Pringsheim as subordinate to Saprolegnia ; the aquatic 

 species having been studied before the terrestrial. The 

 genus is a small one (18 species) though of world- wide 

 distribution. Butler found in pond-water in India the 

 same species as he had found in England. Pythium affords 



