186 THE CHIEF SOUTHERN AGRICULTURAL CROPS 



to the next and when it once makes its appearance in 

 the field, the diseased area continues to spread from 

 year to year until finally the culture of cotton has 

 to be abandoned. 



The disease occurs in many parts of the cotton belt, 

 but has been most destructive in the famous Sea 

 Island cotton region along the coast of Georgia and 

 South Carolina. At one time it seriously threatened 

 to prevent the culture of this crop on many of the 

 lands best suited to it. Officials of the Department 

 of Agriculture were detailed to study the disease, 

 and they observed occasional plants in the infected 

 areas that remained healthy and vigorous through- 

 out the season. Seed was saved from these plants 

 and in the course of a few years a resistant race 

 was developed, by selection, which possessed almost 

 complete immunity from this disease. Strains of re- 

 sistant upland cotton have also been found, so that it 

 is now possible to grow full crops of cotton on lands 

 that are thoroughly infested by the wilt fungus. 

 This is one of the most striking instances of the 

 possibility of overcoming a serious plant disease 

 by the selection and breeding of immune races. 

 Fungi that are microscopically indistinguishable from 

 the one causing cotton wilt produce similar diseases 

 in cowpeas, watermelons, and various other crops. 

 It seems to be a fact, however, that the disease is not 

 usually communicable from one of these crops to an- 

 other. No methods have been discovered for treat- 

 ing these wilts by topical applications. 



Another disease known as root rot (^Ozoyiium') causes 

 the wilting of cotton in certain portions of Texas. It 



