244 



Nature-Study Agriculture 



Fungous 

 diseases 

 of plants; 

 the damage 

 they cause 

 to crops 



Insecticides 

 and fungi- 

 cides 



giving the mold its peculiar color. Unlike bacteria, the 

 fungi do not reproduce by means of division. However, 

 some bacteria at times reproduce by means of spores. 



Most diseases of plants are caused by fungi, while 

 most diseases of animals are caused by bacteria. Mildew, 

 so often seen as a white powdery substance on the leaves 

 of roses, is a fungus. The black smuts of corn, wheat, 

 and other grains are fungi (Figs. 194, 195, and 196). 

 Rust, which sometimes is so plentiful on grain that it 

 rubs off as a brown powder, is also a fungus. It has 

 been estimated that the yearly crops of the United States 

 would be worth five hundred million dollars more than 

 they are if it were not for the fungous diseases of plants. 

 A large part of this loss could be avoided, for many of 

 these diseases are preventable. The chemicals used to 

 prevent the growth of fungus are called " fungicides," 

 as sprays used to kill insects are called " insecticides." 



FIG. 195. The effect of smut of oats on grains. 



U. S. D. A. 



