THE FUNGI: ASCOMYCETES AND BASIDIOMYCETES 311 



believe that a natural hybrid between U. avenue and JJ . levis frequently occurs 

 in nature. From experimental cultures it has been shown that such a 

 hybrid assumes the appearance and mode of infection of U. avenae. 



The life-cycle of Ustilago is represented by the following diagram 

 (Fig. 304) :— 



Basidium 



Basidiospores 



Brand Spore 



Diploid Mycelium 



Monopioid Myceliun) 



Monoploid Mycelium 

 Fig. 304. — Life-cycle of Ustilago. 



Importance of the Smuts to Agriculture 



In former times losses due to Smuts not infrequently amounted to as 

 much as 50 per cent, of the crop. The practice in modern times of dressing 

 the seed with a solution of i fluid oz. of formalin to 2 gals, of water has 

 reduced the loss to a very small percentage. 



Particularly in America, Bunt or Stinking Smut, due to a closely allied 

 genus, Tilletia, is probably a far more important disease. In this case the 

 grains are invaded and the chlamydospores are liberated as in Covered 

 Smut. The same formalin treatment is recommended in this case. 



A number of biologic races of Smut Fungi have been described. It 

 is not possible to go into the details here, but it is sufficient to point out that 

 a strain which may cause a heavy grain loss in a particular variety of Oat may 

 cause practically no infection in another. For example, a certain strain of 

 U. avenae is found to cause high infection in the Oat variety called " Goth- 

 land," but seldom infects " Monarch," while, on the other hand, a certain 

 strain of U. levis infects " Monarch " but not " Gothland." As a result 

 of hybridization certain biologic races were obtained, some of which attacked 

 one and some the other of the two Oat varieties mentioned. 



