284 THE BOOK OF CORN 



Corn smut is caused by a fungus known to bota- 

 nists by the name of Ustilago zeae. It is a fungus of 

 simple structure and habits, entirely distinct from the 

 smuts of sorghum, broom corn, wheat, oats ; barley, 

 millet and those of many other wild and cultivated 

 plants. It affects any part of the plant above ground, 

 forming large pustules, at first of a whitish or grayish 

 color, and finally black by exposure of the mass of dark 

 fungous spores. On the left every kernel (see Fig 79) 

 is destroyed, and the growth of the outer part of the 

 ear has been checked by the disease. On the right 

 only the outer half of the ear is affected, the remainder 

 having perfect kernels, unaffected with smut, and 

 which might be planted without danger of transmitting 

 smut to the next crop. From photographs loaned bv 

 the Indiana experiment station. 



When the corn plant becomes inoculated with the 

 disease, the infection does not spread to all parts of 

 the plant, but remains local, so that each pustule repre- 

 sents a separate infection. The fungus does not grow 

 upon the surface, but inside the tissues, and by the 

 irritation that it sets up causes the tissues to swell and 

 form a pustule, the size depending upon the amount 

 of nutriment that the fungus can extract from the 

 plant, and the rapidity with which that part of the 

 plant is growing at the time. For these reasons the 

 ears usually bear the largest masses of smut. 



For one hundred and fifty years or more it has been 

 the practice of farmers in Europe to treat seed wheat 

 with blue vitriol to remove smut from it, and in late 

 years a variety of practical and efficient methods for 

 the treatment of seed grain have come inco general 

 use in both Europe and America. Until recently it 

 lias been assumed that corn smut might be prevented 

 by similar means, and it was not until the life history 

 of the corn smut fungus was fully worked out by 



