86 



FUNGI AND FUNGICIDES 



externally of a small spherical case, from which project 

 fifteen or twenty, or sometimes more, rather lm^ drli- 

 cutc appendages with recurved tips, as seen in c. Fiir. 4'1. 

 This is the outer spore-case (which botanists call the 

 peritltccium). If it be crushed it will break open on 

 one side, and there will be pushed out about half a 

 dozen small, oval, flattened bodies the inner spore 

 cases, or asci within which may be seen from four to 



FIG. 42. POWDERY MILDEW. MAGNIFIED, 

 a, Peritliecium; b, mycelium; <, germinating spore. 



six small bodies, which are the winter spores. By 

 means of these the fungus passes through the winter. 



Microscopic Characters. A good idea of the 

 structure of this powdery mildew may be obtained from 

 Fig. 42. A small piece of the mycelium running over 

 the surface of the leaf is represented in b; on the lower 

 side are two of the peculiar suckers which penetrate the 

 tissues of the host-plant to draw out nourishment for 

 the fungus, and on the upper side are represented the 

 vertical branches from which the summer spores are pro- 

 duced, as well as one loose spore. In c one of these 



