FIBER PLANTS 



399 



and die. A single leaf often presents the three conditions, 

 green (healthy), yellow (sick), and brown (dead), side by 

 side in bands, parallel to the main ribs and radiating from 

 the leaf stem. The dead parts may break away, leav- 

 ing the leaf ragged. The upper leaves follow rapidly over 

 the course of the lower leaves. The leaves as soon as badly 

 affected fall away, leaving only a bare stalk. In mild cases, 



Fig. 173. 



-A variety of cotton resistant to the wilt ; note the complete failure of 

 the other varieties. After Orton. 



where the disease runs its course more slowly, the intervals 

 between the different stages are more prolonged. In light 

 sand the disease may progress very rapidly and may con- 

 sist of only two stages, the sudden wilted condition followed 

 by speedy death. The final diagnostic symptom of the dis- 

 ease, however, as in the case of many other wilts, is the 

 darkening of the affected veins, which change from the 

 normal white to light brown or black. Though in most 

 cases the plant dies, occasionally one revives and seems to 



