86 



FUNGI AXD FUis^GICIDES 



externally of a small spherical case, from which project 

 fifteen or twenty, or sometimes more, rather lon^ deli- 

 cate appendages with recurved tips, as seen in a, Fig. 42. 

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

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

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

 dozen small, oyal, flattened bodies — the inner spore 

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



FIG. 42. POWDERY MILDEW. MAGXIFIED. 

 a, Perithecium; b, mycelium; c, 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 

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

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

 side are two of the peculiar suckers which penetrate the 

 tissues of the host-plant to draAV 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 



