DETAILED ACCOUNT OP SPECIFIC PLANT DISEASES 563 



does considerable damage (Fig. 204). The fungus is confined to 

 the wheat plant, although nearly all the varieties of that cereal are 

 susceptible to it and under all climatic conditions. The production of 

 spores in the host is confined largely to the ovules, and as these begin to 

 grow, they become smutted. Such smutted grains cause a flaring of the 

 spikelets and diseased parts may be recognized by a slight difference in 

 color. With the formation of the spores, a penetrating and disagree- 

 able odor arises, the presence of which gives the common name to the 

 disease. The smut spores, or chlamydospores, are brown in color, 

 nearly spheroid in form and vary from 16 to 25/x in diameter. From 

 these chlamydospores on germination acicular or needle-shaped basidio- 

 spores (sporidia) arise, which are produced in the form of a crown on a 

 short basidium (promycelium). The spores may unite in pairs and 

 secondary basidiospores be formed. 



This disease can be controlled by the use of formalin. The grain 

 of wheat should be sprayed with the solution (i pint to 30 gallons of 

 water). 



Another wheat smut fungus is Ustilago tritici (Fig. 205). 



