METHODS OF CONTROL 187 



nevertheless, resistant varieties are often 

 the only protection against complete an- 

 nihilation of a species by disease. In pass- 

 ing through a sick field, one cannot help 

 but notice that not all the plants of the 

 same kind are subject alike in the same 

 way to the disease. Some are killed out- 

 right; others are partly affected, or if badly 

 affected, resist the disease; and still others 

 are not at all diseased. If, therefore, we 

 are able to select the seed from the resistant 

 strain and multiply it rapidly, we will ob- 

 tain resistant plants capable of producing 

 100 per cent healthy plants in a sick soil. 

 That this is possible there can be no doubt. 

 A strain of cowpeas has been obtained 

 which is resistant to wilt, and a strain of 

 clover has also been obtained which is re- 

 sistant to anthracnose. Of course, it can- 

 not be expected that a strain will be re- 

 sistant to every disease, but there is no 



