142 FARM SPIES 



plants on which the aphids cannot feed, the weeds 

 have little chance to grow during the winter. They 

 are cleaning crops because they clean the fields of 

 weeds and aphids. Many farmers call them cover- 

 crops because they will take up the plant-food and 

 hold it so it cannot waste during the winter ; they 



FIG. 59. "The weeds have little chance to grow during the winter." 



also hold the soil-moisture and keep the soil from 

 washing during heavy rains. You can see how 

 important it is to use these cover-crops even when 

 you have no aphids. Let us take, for example, this 

 farm on which Mr. Gardner grows cotton, corn, and 

 oats as the main crops. Oats planted in the fall 

 keep down the weeds during the winter, and since 



