166 _ The Sweet Potato 



destroyed. The same precautions should be used for 

 this form of the disease as for soft-rot. 



DEY-EOT (Plates YII, VIII) . 

 (Diaporthe batatatis) 



This rot begins at one end and slowly works toward 

 the middle of the potato or to the other end. This 

 results in a firm hard brown rot which causes the potato 

 to look dry and mummified. Small dome-like bumps 

 are just noticeable to the naked eye ; if the outer surface 

 of the skin is scratched away, the tissues beneath present 

 a coal black appearance. In the small protuberances 

 on the surface are to be found millions of colorless 

 spores, which serve to reproduce the fungus. 



While dry-rot attacks the stems of the plants in the 

 field and draw-bed as well as in the storage-house, yet 

 it is by no means the most serious of the rots. It is 

 widely distributed throughout the country, and usually 

 does some damage wherever found. 



JAVA BiACK-EOT (Plate VII) 



(Diplodia tubericola) 



This rot receives its name from its first discovery in 

 this country on a shipment of sweet potatoes imported 

 from Java. The disease is widely distributed, but is 

 most common in the South. Potatoes attacked by this 

 disease become dry, hard, brittle, coal black inside, and 

 hard to break. Java black-rot usually begins at one end 

 and develops very slowly, requiring several weeks com- 

 pletely' to destroy a tuber. The surface of the potato is 

 very rough, the skin becoming wrinkled and knots or 

 protuberances abundant over it. 



