FIBER PLANTS 185 



the plant is shown by the fact that richer places in 

 the field, as for instance old fence rows, always show 

 a considerable immunity, and further that the disease 

 can be quite effectively controlled by incorporating 

 more vegetable matter in the soil and by applying pot- 

 ash. On many soils the application of from a hundred 

 to two hundred pounds of kainitper acre will act almost 

 as a specific. Tlie excessive use of phosphoric acid 

 without potash greatly increases the injury. On land 

 subject to rust the disease can be quite perfectly con- 

 trolled by following a rotation like that suggested on 

 page 145, which shall provide for at least one crop of 

 cowpeas between cotton crops, and by the use of fer- 

 tilizers rich in potash. In other words, the appearance 

 of rust is a sure indication of soil exhaustion. 



Cotton wilt (^Neoeosmospora) or Frenching, as it is 

 sometimes called, is due to the growth of a fungus 

 within the tissues of the stem and roots. Affected 

 plants soon become somewhat dwarfed and the leaves 

 assume an unnatural aspect, sometimes being streaked 

 with yellow or brown. Usually after a time the 

 whole plant suddenly wilts and in a few days dies. 

 When only a part of the stalk is affected, the plant 

 may linger throughout the season and even produce a 

 partial crop. The fungus develops principally along 

 the ducts in the vascular bundles, where its presence 

 can be detected by the brown staining of the bun- 

 dles, which is easily seen when cutting off the diseased 

 stem. The sudden wilting occurs when the fungus 

 develops so rapidly as to plug these ducts and thus 

 prevent the upward flow of sap from the roots. This 

 funofus is able to live over in the soil from one season 



