Cereals 



285 



sheaths of the leaves hold water, and inclosing as they do 

 the tender growing portion of the stem, are admirably suited 

 to infection. Since infection cannot occur without moisture, 

 weather conditions are of predominating influence. 



Fig. 149. — Smut upon sweet corn tassels. After Jackson. 



The longer the crop grows, the longer the period of sus- 

 ceptibility is maintained. Thus a late-planted crop in In- 

 diana showed half as much infection as a crop which was 



