Fiber Plants 349 



Angular leaf-spot ^'"^' ^"' (Pseudomonas malvacearum EFS). 

 — This disease was first described in 1891, and is widely 

 distributed in the cotton producing states, in Natal and 

 the West Indies. The diseased areas appear as angular 

 leaf-spots bounded by the veins and are of a watery ap- 

 pearance. They may be scattered over the leaf, or they 

 may be nearly contiguous and later become confluent, 

 resulting in irregular dead patches. Frequently they are 

 most numerous adjacent to the main ribs, and result in 

 long, irregular, dead, black regions. The dead tissue is 

 brittle and often falls away, causing holes or ragged edges. 

 Badly affected leaves fall early and loss of 50 or 60 per cent 

 of the leaves is not unusual. When on the boll, the spots 

 may be a centimeter in diameter, and the seed may become 

 infected. Seedlings from such seed are stunted and the 

 stand poor. Cankers occur on the stems of young plants. 

 Seed should be taken only from healthy plants. Treatment 

 of seed with concentrated sulfuric acid to remove the lint, 

 followed by either the mercuric chlorid or the hot-water 

 treatments may be employed to advantage. 



Damping-ofif (Pyfhium debaryanum and other fungi). — 

 Young cotton plants may suffer the characteristic soft rot 

 of dam ping-off. 



Sore-shin (Corticium vagum, Rhizoctonia) . — Primarily 

 this is an ulcerous wound upon the stem near the ground, 

 accompanied by reddening or browning of the leaves. If 

 the ulcer enters deep into the stem, so as to interfere with 

 the ascending sap, it may cause death, though the wound 

 usually heals before the disease has progressed far. The 

 disease is often caused by the attack of Rhizoctonia, espe- 

 cially in tissues predisposed to such attack by weakness. 

 Harrowing, to aid in drying the surface soil, to some extent 

 prevents the attack and development of this fungus. 



A similar disease may also result from purely mechanical 

 injuries caused by tools. 



Smut {Doassansia gossypii Lag.) occurs on the leaves in 

 Equador and the West Indies. Rust {Kuehneola gossyyii 



