64 FUNGOID DISEASES 



an obligate parasite^ ; when its spores germinate on 

 the surface of the leaf, the germ tube branches and 

 rebranches, forming the wool-like growth. The 

 mycelium does not enter the plant, but special 

 organs called haustoria (see p. 5) draw nutriment 

 from the host for the fungus. The spores are 

 formed in chains from short branches of the mycel- 

 ium, in a similar manner to E . graminis (Fig. 16). 

 When carried by the wind to the surface of healthy 

 leaves they readily germinate,^ thereby setting up 

 new centres of infection. Later small, brownish 

 bodies about the size of a pin's head are formed on 

 the mycelium on the surface of the wilted dying 

 leaves. These little bodies gradually become 

 black ; they are the perithecia containing asci in 

 which the ascospores are formed and enclosed. The 

 ascospores are set free and carried by the wind to 

 healthy young plants in the spring. 



(h) False Mildew [PeronospoJ'a Trifoliomm and 

 Pe7'onospora vicice). Class : Phycomycete/E ; Order : 

 Peronosporales. 



Peronospora Trifoliorum causes false mildew of 

 clover and lucerne especially, but is also found on 

 other plants. 



P. vicicB causes false mildew on various leo^um- 

 inous plants, particularly vetches and peas. Both 



^ The spores may be germinated on certain artificial media, but 

 the germ tube soon dies, in fact it is, up to the present, impossible to 

 grow the fungus as a saprophyte. 



