288 THE BOOK OF CORN 



tions for completing the whole cycle of growth, no 

 resting period being essential. 



Observations carefully tabulated have shown that 

 the pustules become more numerous in a field of corn 

 as the season progresses, unquestionably due to suc- 

 cessive infections. Early planted corn is liable to show 

 more smut at the end of the season than late planted, 

 simply because it has had a longer period in which to 

 become infected. Corn planted upon extra rich or 

 extra moist soil is more liable to infection, because the 

 rapid growth exposes more surface of tender tissues 

 and for a longer time. It must be remembered that the 

 secondary spores are only able to push their germinal 

 tubes into soft tissues. They sometimes effect an en- 

 trance into the tips of the brace roots before these enter 

 the ground. They attack any part of the leaf when 

 immature, and also the tassel, especially when the stam- 

 inate flowers first appear. The lower part of each 

 internode of the stem, just above the joint and inside 

 the sheath, is particularly vulnerable throughout almost 

 the whole season, for com, in common with other mem- 

 bers of the grass family, continues to grow and elon- 

 gate at this point for an indefinite period. On the left 

 (see Fig So, showing smut affecting the tassels) the 

 smut spores were washed in among the unfolding 

 leaves at the summit of the stem before the tassel 

 emerged, and the base of the leaves as well as the 

 tassel became diseased, so that growth of the tassel 

 was checked. On the right the infection took place 

 after the tassel unfolded, and gained entrance through 

 the open staminate flowers. 



Not only are the tissues delicate here, but the 

 sheaths retain moisture and provide the spores, that 

 drop in from above or are washed down bv rains or 

 dews, good opportunity to germinate and pierce the 

 plant. Smut often starts where the stalks are injured 



