THE INSECTS. 131 



to our cultivation and after all make very little 

 if any impression ; the wilderness is behind and 

 the supplies from that source may come upon us 

 even were it possible to eradicate every pest from 

 our fields. 



-Clean cultivation, however, does something to 

 diminish the plagues, and here also the careful 

 study of economic insects comes in. Unless we 

 know them we are left in the position of the 

 cotton-grower who once spoke of " the blast " and 

 " the shrivel " as responsible for the failure of his 

 crops. With only vague notions of causes we can 

 hardly expect to do anything at all. " Knowledge 

 is power " in this as in many other things. 



