PLANT DISEASES 



233 



of species ; hence plants of one kind may be grown without 

 danger close beside other kinds that are diseased. These 

 organisms that cause disease are usually given the name of the 

 effect they produce. Among the more familiar are the rots, 

 smuts, rusts, mildews, blights, 

 and wilts. Often the causal 

 organisms are not closely re- 

 lated, but if they produce simi- 

 lar effects, they are likely to be 

 named accordingly, just as a 

 rise in temperature in man is 

 called a fever, no matter what 

 its cause. Some of the more 

 common plant diseases are men- 

 tioned here ; others may be 

 found described in the reports 

 of agricultural experiment sta- 

 tions and in manuals devoted 

 to the subject. 



Rots. Many kinds of fruits 

 and vegetables are attacked by 

 rots which cause their tissues to 

 break down into a watery mass 

 and thus spoil the specimen. 

 Good examples are found in the 

 rot of apples and other fruits, 

 carrots, cabbage, and the like. The wet rot of potatoes is 

 another familiar form. Rots are caused both by bacteria 

 and other fungi. 



Wilts. The wilts are readily recognized from the fact that 

 the leaves of the plant attacked begin at once to droop and 

 soon after the death of the individual ensues. In many cases 

 the wilting is caused by the fungus growing in the ducts of 

 the plant and thus shutting off its supply of moisture. 



FIG. 170. Mildew of cherry 



From Duggar's " Fungous Diseases 

 of Plants " 



