MILDEW 



213 



fungi are great destructive agents. Often they destroy 

 substances useless to man and at the same time convert 

 part of those substances into useful products. The work 

 of converting organic matter 

 into humus is an instance. 



The chief reason, however, 

 why we are interested in fungi 

 is on account of their work in 

 destroying useful crops. Of 

 such harmful fungi we have 

 space to notice in detail only 

 mildews, smuts, rusts, scabs, and 

 molds. 



158. Mildew is a fungous dis- 

 ease to which all the higher 

 plants are subject. The well- 

 known " potato blight " may be 

 taken as a type of the mildews. 

 This disease is found over the 

 entire world wherever the potato 

 is grown, and in America alone 

 it causes an annual loss equal 

 to several millions of dollars. 

 In Ireland, in 1845, its complete 

 destruction of the potato crop 

 caused a terrible famine. 



When first attacked by mil- 

 dew, the edges of the potato 

 leaves appear water-soaked, and 

 have a faint purplish tint. 

 As dry weather comes on, the 

 affected parts turn brown. Later, the entire leaf becomes 

 affected. Mildew spores, which correspond to seeds among 

 the higher plants, are developed in great numbers. These 



ANTHRACNOSE ON BEAN POD. 

 A fungus blight. 



