PARASITIC FUNGI 



FIG. 17. Pythium. A, hyphae in tissue of seedling; sp., 



sporangium. B, ditto, more highly magnified. The hyphae (h) 

 have penetrated the cell walls (c.w.) through narrow holes whicl 

 the growing tips have bored out. C, branched hypha emerge 

 into the air, forming sporangia (sp.). D, germination 

 sporangium in water. The contents have divided to form 

 number of zoospores which are enclosed in a bladder pushec 

 through a hole in the wall ; z, free zoospore ; z germinath 

 zoospore. E, sexual reproduction (conjugation) ; a, youi 

 female organ (spherical) and male organ (club-shaped) in contact 

 b, penetration of male organ ; c, fertilised egg (zygote) surrounde 

 by thick wall, male organ empty. F, germination of zygol 

 in water (similar to D). G, cress seedling attacked by Pythii 

 just above the soil surface. (After Marshall Ward, etc.) 



