Family Convolvulace^e 173 



three quarters of a million for the entire sweet potato 

 crop of the United States. > 



CHARCOAL ROT 

 Caused by Sclerotium bataticola Taub. 



"Charcoal rot" is a new name for an old trouble. 

 It is mainly a storage trouble and is found most com- 

 monly in overcrowded houses and in bins nearest the 

 stoves. It is especially plentiful in houses which 

 lose heavily from soft rot. After the work of Hal- 

 sted, from 1890 to 1913, the fungus which caused 

 charcoal rot was believed to be a stage of the black 

 rot fungus. But it has been shown by the writer that 

 charcoal rot is a distinct disease and that the fungus 

 which causes it is in no way connected with or re- 

 lated to the black rot organism, Sph&ronema fim- 

 briatum (E. and H.) Sacc. 



Charcoal rot is commonly mistaken for black rot. 

 While black rot produces only superficial spots on the 

 roots, and does not produce a rot of the entire root, 

 charcoal rot is a disease which penetrates the entire 

 root. The parasite does not produce surface spots, 

 but turns the interior tissue into a black charcoal 

 mass (fig. 27 d) caused by the formation of minute 

 colored sclerotia (fig. 28 m). With the exception of 

 drying and slight shrinkage, there are no external 

 symptoms to distinguish the disease unless the skin 

 is bruised, showing the blackened contents. It can 

 be recognized when the roots have been completely 

 invaded. Recent studies on this disease seem to 



