ORDER PERONOSPORALES 



131 



B 



-m^'-i 





Fig. 41. Peronosporales, Family Pythiaceae. Phytophthora cactorum (L. & C.) 

 Schrot. (A) Aerial filament in moist air, producing sympodially a succession of spor- 

 angia ("conidia"). (B) Formation of zoospores within the sporangium and emission 

 mto a vesicle. (C) Fertilization of oogone. (D) Mature oospore. (E) Germinating 

 oospore. (Courtesy, Blackwell: Brit. Mycol. Soc. Trans., 26(1-2) :71-89.) 



