DISEASES OF PLANTS 



237 



over the leaves. (Cal- 

 ifornia Experiment 

 Station, Bulletin 186; 

 Idaho, 31, 39; Wash- 

 ington, 70, 83.) 



SMUTS 



The smut of corn 

 forms on the ear and 

 other parts of the 

 plant large white 

 masses which open 

 and send out great 

 clouds of blackspores_ 

 (figure 137). For- 

 merly the grains of 

 corn were treated 

 with a germicide to 

 prevent smut, but this does no good, because infection 

 may take place on any very young part of the corn plant. 



With the smuts of grain (black smuts of wheat, oats, 

 barley, and rye, stinking smut of wheat) infection takes 

 place only very soon after germination, and mainly 

 from spores on the grains. Hence they can be pre- 

 vented by treating the seed with bluestone or formalin. 

 The seeds must be covered by the solution long enough 

 to get thoroughly wet (wheat for a few moments ; oats 



FIG. 136. Oidium or powdery mildew on 

 grapes, causing a whitish appearance. 



