454 DISEASES OF ECONOMIC PLANTS 



The tips of the leaves are often frayed. 



Volutellose (Volutella concentrica Halst.). — Numerous 

 lemon-colored acervuli surrounded by concentric bluish 

 rings render these spots different from those above 

 described. 



CALLA 



Soft rot,^ bacillose (Bacillus aroidece Townsend). — A 

 large annual loss and frequently the abandonment of calla 

 growing is due to this disease, which is known through- 

 out the United States, and which is perhaps identical with 

 the carrot soft rot.^ 



The affected plants rot off near the soil surface, and the 

 rot progresses from this point up into the leaves or down 

 into the corm. Usually the rot first shows at the top of the 

 corm, but in some instances it is seen first at the edge of a 

 petiole, or on the corm below ground. 



In section the diseased portion is brown, soft, and watery. 

 Leaves whose bases are diseased become pale at the edges, 

 then brown. Similar changes occur in spots on the leaf, and 

 the whole leaf eventually dies, or the rot may progress so 

 rapidly that the leaf falls before losing its green color. 

 The flower or its stalk are similarly diseased. Through 

 the corm the roots are reached. Here the sldn is unaffected 

 and remains as a parchment-like tube filled with the creamy 

 residue of decay. Rot of the bulb may be arrested by 

 unfavorable conditions and show only as dark sunken spots. 



1 Townsend, C. O., U.S. Dept. Agr. Bur. Plant Indus. Bui. 60, June, 

 1904. 



^ Harding, H. A., Jones, L. R., and Morse, W. J., N.Y. (Geneva) Agr. 

 Exp. Sta. Tech. Bui. 11. 



