158 Minnesota Plant Diseases. 



Smuts very often possess the power of stimulating their host 

 plants to abnormal growth. Thus in the corn smut, the attacked 

 part of the corn plant swells up into a tubercle many times larger 

 than the original plant part. The advantage of this to the para- 

 site is obvious, for it increases many-fold the area of the feeding 

 ground as well as the spore-producing area. Such tubercles in 

 corn smut are found on leaves, young stems and on kernels and 

 even in the tassels. 



In some smuts the stimulation is exerted on the rudiments 

 of organs which are not normally produced in certain flowers 

 causing the rudiments to develop into mature organs. Such is 

 the case in certain pistillate flowers of the Pink family where 

 the smut stimulates the rudiments of the stamens to mature de- 

 velopment. 



The smuts are parasites, chiefly of the flowering plants and 

 particularly of the grass family. One smut, however, inhabits 

 the capsule of the peat moss plant. The choice of organs for 

 the establishment of the parasitic mycelium varies with different 

 smuts. A very large number live in the grains and seeds of 

 plants, where they get both advantage of position for spore dis- 

 tribution as well as an abundant supply of food material. 

 Sometimes a whole inflorescence is destroyed. The floral parts 

 are also attacked by smuts, e. g., certain smuts fruit only in the 

 anthers of species of the carnation family, forming their spores 

 in place of the pollen so that when the flower opens a violet 

 smut dust is discharged from the anthers instead of the pollen 

 dust. Leaves of the host plant are commonly attacked and are 

 often swollen on account of the stimulation of the parasite. 

 Stem parts may be attacked and one smut is known in Minne- 

 sota to produce its spores in the roots of certain rush-like plants. 



Almost every cereal plant is subject to the attack of one or 

 more smuts and many of the wild grasses are likewise invaded. 

 The common corn, oat and wheat smuts are best known. 

 Many garden plants such as onion and violet are subject to 

 smut attacks and this is also true of many members of the Pink 

 family, where the smut often lives in the anthers of the flowers. 



The dock family of flowering plants is also peculiarly subject 

 to smut attacks and this is also true of the pink family. Other 

 flowering plants are attacked but not so commonly as the above 

 mentioned groups. (Figs. 27, 71, 72, 146 to 151.) 



