228 



FUNGOUS DISEASES OF PLANTS 



XXVI. MILDEW OF COMPOSITES AND OTHER PLANTS 

 Erysiphe Cickoracearum De C. 



This species of mildew is also widely distributed and occurs 

 upon more than two hundred hosts of numerous families. It is 



unusually common upon spe- 

 cies of Compositae and in 

 general is easily the most 

 destructive fungus of these 

 hosts. It is also well known 

 to the florist upon species 

 of phlox and to the gar- 

 dener upon some varieties 

 of cucurbits. 



Tne fungus is often con- 

 fused with the previous spe- 

 cies. The perithecia are 

 about equal in size, but the 

 appendages of this form 

 are usually short. The asci 

 are numerous (often 10-15), 

 and Salmon considers that 

 the central specific charac- 

 ter lies in the possession of 

 two spores. Nevertheless, 

 this species is also variable 

 in every character, and it 

 will not be easy to distin- 

 guish morphologically between certain forms of the two species. 



FIG. 93. MICROSPH&RA ALJV/, PERSISTENT 



FORM ON OAK. (Photograph by Geo. F. 



Atkinson) 



XXVII. MILDEW OF WOODY PLANTS 

 Microsphcera Alni (Wallr.) Wint. 



This variable species is typically a fungus of a variety of 

 woody plants. It is common upon amentiferous trees and shrubs, 

 but popularly is doubtless best known as the lilac or syringa 

 mildew. Upon the lilac the mycelium covers the entire leaf. 

 So constant is its occurrence upon this host during the late 



