166 Diseases of Truck Crops 



sound, but failed to grow when planted. Upon 

 examination the roots were found to be rotted. The 

 fungus which caused the rot was sent to Ellis, who 

 identified it as a new genus and gave it the name of 

 Lasiodiplodia tubericola. Sweet potatoes brought 

 from Java in the spring of 1895 were found to be 

 affected with the same fungus when they were re- 

 ceived at Baton Rouge. This seems to indicate that 

 the fungus was introduced in the United States from 

 Java. 



Symptoms. Sweet potatoes affected by the fungus 

 show dark shriveled patches over which are scattered 

 numerous pycnidia. These emit either mature one- 

 septate dark spores of Diplodia type, heaped to- 

 gether, or white strings (fig. 26 f), which are made up 

 of hyaline Macrophoma spores, or both (fig. 26 f). 

 In making longitudinal sections through different 

 stages of affected roots, it will be found that the fun- 

 gus attacks the interior tissue, beginning at the point 

 and gradually invading the whole of the interior of 

 the root. The infected tissue is jet-black (fig. 26 e), 

 somewhat resembling the charcoal disease. In- 

 fected roots dry and shrivel and become brittle. 

 Complete rotting of the root is effected in four to 

 eight weeks. The active enzyme from the fungus 

 precedes the mycelium some distance, for in a longi- 

 tudinal section of a newly infected root two zones 

 may be observed, one, a dark area which is occupied 

 by the fungus, and the other, a brown zone which 

 precedes the dark patch in which the mycelium is 

 absent. The pycnidia are born singly or in groups 



