Minnesota Plant Diseases. 297 



Loose smut of wheat [Ustilago tritici (Pers.) Jens.']. This 

 smut is also known as wheat brand. It is a destructive smut of 

 wheat and differs in many ways from the stinking smut. It can 

 be distinguished, botanically, by the behavior of its spores since 

 they develop at germination a chain of cells similar to the loose 

 smut of oats, instead of an undivided tube, as in stinking smut 

 of wheat. From this chain of cells are budded off the secondary 

 spores, which behave as do those of loose smut of oats. In other 

 characters, which are visible to the naked eye, this smut is well 

 marked off, from the stinking smut of wheat. The smut masses 

 are formed in the place of the grains, and may even supplant the 

 chaffy scales. This smut mass does not remain closed until har- 

 vest time, but opens at flowering and the spores are scattered by 

 the wind. At harvest time, therefore, only the bare stalks of the 

 wheat heads, with remnants of scales, remain on the plants. This 

 method of distribution gives rise to the common name of loose 

 smut. The spore mass is a dark, olive-green, dirty mass which 

 differs from the stinking smut in the absence of any fetid odor 

 such as the latter possesses. 



No sure method of prevention is known. A modification of 

 the Jensen hot water process for loose smut of oats has given 

 some relief, but seems to injure the seed. The formalin method 

 is also uneffective. The only relief known at present is the selec- 

 tion of clean seed, which can only be done by obtaining the seed 

 fr< 'in a smut-free district. (See Fig. 72.) 



Corn smut [Ustilago niaydis (DC.) Cda.]. The smut of corn 

 is a disease familiar to every farmer. It may attack almost any 

 part of the plant, but is particularly abundant upon the cobs, 

 staminate tassels and the leaves. When a cob of corn is attacked 

 a number of the grains become enormously enlarged and are 

 covered with a thin, whitish-grey membrane. The whole cob 

 may thus be enlarged to twice its natural size. The interior of 

 the affected grains is filled with a blackish to dark green pow- 

 der of smut spores. When a leaf is attacked, tumor-like swell- 

 ings are produced, which often become as large as an apple and 

 this tumor contains the blackish spore-powder. Upon the 

 staminate tassels, smaller tumors are formed which are of a 

 similar structure to those of the leaf. The smut spores rest 

 through the winter. In the spring they germinate, producing 



