320 DItiEASES OF ECONOMIC PLANTS 



205 of these are found in the United States, growing upon 

 some 442 different kinds of plants.' 



Most smuts are upon unimportant, uncultivated plants. 

 Some of them, such as the cam smut, onion smut, and the 

 smuts of loheat, oats, rye, barley attack plants of high eco- 

 nomic value and cause great damage. The common corn 

 smut develops upon almost any part of the corn plant, 

 but is usually most conspicuous upon the ear and tassel. 

 Onion smut grows upon the leaves, often in the bulb; rye 

 smut in the stem; that of oats, wheat, and barley in the 

 ovary, the grain. Another smut of corn growing upon 

 the tassel is less widely kno^vn. 



It is evident that to know precisely at what parts and 

 at what periods the various crop plants are open to infec- 

 tion is of utmost importance in looking to the prevention 

 of the smuts. It was early proved that oats are suscep- 

 tible to infection only in the very young periods of their 

 development. Kuehn and Wolff held opposing views as 

 to whether it is the young stem or the first leaf sheath that 

 is susceptible. The very exact work of Brefeld settled 

 this point beyond all controversy. He also proved that 

 corn is susceptible to infection on all young, tender, growing 

 parts, and recently Maddox, Brefeld, and others have 

 shown that in the case of the loose smut of wheat and the 

 barley smut infection occurs while the plant is in bloom, 

 this infection affecting the seeds and resulting in smutted 

 plants in the crop raised from such infected seeds. 



It is upon these facts that our present modes of preven- 

 tion are based. The treatment for oat smut is such as to 

 kill the spores adhering to the grain and thus prevent in- 



' Clinton, G. P., Proc. Boston Soc. Nat. Hist. 31, 334, 1904. 



