io6 



THE WHEAT INDUSTRY 



air and the spores appear on the outside. Rust 

 spores then appear upon the leaves. Smut spores, 

 which appear about the time when the wheat is in 



flower, cover the spike. 

 Spores have the same 

 relation to parasitic 

 plants that seeds have 

 to higher plants ; and, 

 since they are innu- 

 merable, these diseases 

 spread rapidly. Smut 

 spores attack the grain 

 in different ways. 

 Sometimes they fill the 

 grain, making what 

 are called smut balls. 

 Sometimes only the 

 stem of the plant is 

 affected. This weak- 

 ens the plant and 

 consequently the grain 

 yield is small. Rust 

 living within the plant 

 does its damage by 

 using the food ma- 

 terials which are neces- 

 sary for the growth of the host. In this way the 

 wheat plant is weakened and a low yield and 

 shriveled grain is sure to result. 



From Plant Diseases Freeman. 



FIG. 63. Stinking smut of wheat : 

 /, an infected spike ; 2, smut infected 

 spikelet ; 3, smutted kernels. 



