CROP ENEMIES AND FRIENDS 



199 



suffering from crop shortages and failures. If the wheat crop of 

 the United States be small, the surplus of Russia furnishes us 

 bread. If America has a bountiful crop, it goes to supply food for 

 Europe. 



Disadvantages. But this intercourse has its disadvantages. 

 As you learned, many troublesome Old World weeds have been 

 brought to us in one way and another. Other and more deadly 

 crop enemies have been imported. Diseases and insects, once 

 confined to localities, have spread over the world. 



Fungous Diseases. Old farmers remember when fungous 

 diseases of crops were almost or entirely unknown. Fruit ripened, 

 vegetables grew, grain matured, without any serious injury. 

 Now there is hardly a farmer who does not lose by these diseases 

 every year. Usually, he loses heavily unless he uses preventive 

 measures. 



Fungi. A fungous disease is one caused by fungi, plants 

 which live on other plants or animals and take nourishment from 

 them. One such plant is called a fun'gus. Some 

 fungi, such as mushrooms, are large ; others, such 

 as blight, are very small, so small that they are 

 invisible to the naked eye. Some, such as the 

 yeasts, are useful; others, such as the smuts, are 

 harmful. Some cause deadly diseases; without 

 others, man would die, because it would be im- 

 possible to raise any food crop. 



Three well-known classes of fungi are mold, ^ 



yeast, and bacteria. MoLD 



Fungi are the lowest forms of living things. Great]y magnified 

 They lack the chlorophyl by means of which, as 

 you have learned, higher plants feed 'on the elements of the air. 

 Instead of being green, they are usually white, pink, yellow, blue, 



