332 



DISEASES OF ECONOMIC PLANTS 



brane eventually bursts, loosening a powdery, dry, black 

 mass of spores through which fibrous veins of the com 



plant still pene- 

 trate. It has been 

 conclusively dem- 

 onstrated that the 

 causal fungus is not 

 conveyed to the 

 new crop in the 

 seed, as is the case 

 with so many other 

 smuts, and that 

 therefore no form of 

 seed treatment is of 

 value for its pre- 

 vention. The sow- 

 ing of seed covered 

 with smut spores 

 does not result in 

 any more smut than 

 does the use of un- 

 infected seed. 



It has been clearly 

 shown that infec- 

 tion is produced by 

 the spores which, 

 under suitable con- 

 ditions of moisture, 

 fall upon any tender 

 part of the corn plant. The silks furnish the requisite 

 conditions, and it is through them that ear infection occurs. 



Fig. 140. — Com smut upon the ear. Original. 



