258 



FORMS OF SMUTS 



related. They produce very generally but one form of spore that 

 may possibly be compared to the teliospore. They are com- 

 mon and exceedingly destructive parasites, affecting especially 

 the flowers and fruits of corn and other cereals as wheat, oats 

 and barley (Fig. 166). The damage by smuts to the corn crop 



FIG. 1 66. 



FIG. 167. 



FIG. ^66. A common smut, Ustilago, transforming the kernels of corn 

 into sootjK.ljlack pustules. 



FIG. 167. The formation and germination of the spore of a smut: A, 

 the formation of the spores from the mycelium in the kernel of corn. B, 

 germination of a spore and the appearance of the basidiospore. 



of the United States exceeds $2,000,000 annually. In the case 

 of corn, the parasite keeps pace with the growth of the plant 

 without producing serious damage until the flowers appear, when 

 the mycelium increases greatly in the affected ears and "tassels" 

 producing sometimes enormous malformation, especially in the 

 ears, which appear as glistening white blisters or pustules. Later, 

 these bodies change to a sooty black, owing to the transformation 

 of the cells of the mycelium (Fig. 167, A) into black greasy spores. 

 These spores are scattered in clouds upon the breaking of the 

 pustules and germinate much after the manner of the telio- 

 spores of the rusts, infesting the young and delicate parts of 



