340 



DISEASES OF CULTIVATED PLANTS 



Maize smut (Ustilago maydis, D. C.) attacks maize or 

 Indian corn, and often seriously interferes with the yield. It 

 forms marked deformations on practically every part of the 

 plant, under the form of large galls or blisters of a whitish 

 colour. When approaching maturity the spore masses appear 



FIG. 101. Ustilago avenae. i, a ' smutted ' ear of oats ; 2, spores ; 3, ger- 

 minating spores ; 4, secondary spores conjugating. Figs. 2-4 highly mag. 



to be of a dark olive-green colour, as seen through the tissues 

 forming the membrane. When mature the blisters burst and 

 liberate a dense powdery mass of black spores. The heads 

 are most frequently attacked, and the galls may attain to the 

 size of an apple, sometimes larger. Infection may occur at 

 any young, growing portion of the plant. 



The spores are irregularly globose, dark brown, delicately 

 spinulose, 9-12 p diam. 



