FIBER PLANTS 401 



disease upon young plants usually follows the use of dis- 

 eased seed. Upon old stems it causes blighting of the 

 bark, which becomes reddish brown and dies. 



Upon the leaves as upon the stems the attack is mainly 

 limited to injured or weak parts. The seed leaves, being 

 in a state of weakness, are especially susceptible to the 

 fungus, which develops here with characters very similar 

 to those of the stem and the boll. The leaves sometimes 

 have a scalded look, assume a yellowish or leaden green 

 color, and wither and die, much as though frosted. 



There is abundant evidence that the disease is largely 

 carried from year to year in the seed. Therefore, only seed 

 from entirely healthy fields and seed that has been ginned 

 where only healthy cotton has been ginned should be used. 

 No mode of seed treatment has proved reliable. 



Texas root rot (Ozonvum omnivorum Shear.). — The first 

 technical description of this disease was given by Pammel 

 in 1888. It has since been the subject of many papers, and 

 is known to occur in very destructive form in Texas, Okla- 

 homa, New Mexico, and Arizona, though it has notsyet 

 been found east of Texas.' The estimated loss from 

 ozoniose in 1906 in Texas was about 13,000,000. Some 

 planters regard it as a worse enemy than the boll weevil. 



In this disease a few of the plants may wilt and dry up 

 in a day. This usually occurs at or before blossoming, 

 occasionally upon plants only a few inches high. Later, 

 many plants suffer similar fate, resulting in irregular spots 

 of disease in the field, marked by the presence of numerous 

 standing, dead plants. The plants succumb with especial 



' Shear, C. L., and Miles, Geo. F., U.S. Dept. Agr. Bur. Plant Indus. 

 Bui. 102, Part V, September 9, 1907. 

 2d 



