GENERAL DISEASES 



67 



The one means of overcoming these soil diseases which 

 is most promising to farmers who own affected soil lies in 

 the discovery of a variety of the crop plant that will not 



Fig. 20. — Root knot (nematode) on salsify. Original. 



succumb to attack even when planted upon sick soil. 

 Varieties of cotton that can resist the cotton wilt, of flax 

 that can resist flax wilt, and of cowpeas that can resist 

 the cowpea wilt have been discovered. There is similar 

 hope in regard to other crops. 



Root knot, Nematode galls. — Root galls, varying from 

 a few millimeters to a centimeter or more in size and super- 



