404 DISEASES OF ECONOMIC PLANTS 



red dots, which finally, as they enlarge, bear brown or white 

 centers with a characteristic red border. A copious de- 

 velopment of dark hyphse upon the centers later gives 

 them a blackish hue, and an abundance of white spores gives 

 these hyphse a white coating. The old diseased centers 

 of the spots are brittle and frequently break away, leaving 

 perforations. The disease is widespread but unimportant, 

 since it is largely limited to weakened tissues, especially 

 to spots produced by cotton mosaic. 



BsLcteriose {Bacterium malvacearum E. F. Smith).— Wide- 

 spread but seldom abundant enough to attract attention, the 

 diseased areas appear as angular spots bounded by the veins 

 and of a watery appearance. 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. 



Boll rot. — This rot in wet seasons may cause the loss of 

 nearly all of the crop. It sometimes begins as small, black 

 or dark brown spots upon the young seed and lint, especially 

 near the base of the boll, and thence invades the whole boll, 

 showing itself externall}^ only when nearly all of the inner 

 part of the boll has decayed. If it begins later, only a few 

 seeds and their Unt may rot, and the remainder of the boll 

 may ripen and be harvested. The cause and remedies are 

 not known. The disease may be of bacterial origin. 



Damping ofif {Pythium DeBaryanuni and other fungi). — 

 Young cotton plants may suffer the characteristic soft rot 

 of damping off. 



