92 



THE FUNGI WHICH CAUSE PLANT DISEASE 



into several distinct species. It is limited to the Compositse, 

 Helianthus and Madia being the only hosts of economic impor- 

 tance. 



Hypophyllous; conidiophores fasciculate, slender, 300-750 n, 

 3-5 times branched, ultimate branchlets 8-15 m long, verticillate 



Fio. 63. — P. viticola. A, section of a leaf with conidiophores emerg- 

 ing from a stoma; C, formation of swarm spores; D, formation 

 of oospores. After Millardet. 



below the apex of the branching axis which is frequently swollen 

 and ganglion-like; conidia oval or elliptic, 18-30 x 14-25 n; 

 oospores 30-32 /i, epispore yellowish-brown, somewhat wrinkled. 



P. ribicola (Schr.) Schr. grows on various species of currants in 

 Europe and America but is probably of but slight economic 

 importance. 



