45 



made. These are of special interest because of the po: 

 the quality of susceptibility or resistance, and studie 

 second and later generations should give further ligbl < 

 eral problem of the inheritance of the resistant quality. 



Physiologic Races of Oat Smuts 

 In the last Annual Report an 

 cialized races of Ustilago Avem 

 ghum and Red Rustproof varieties. Two distinct races were dif- 

 ferentiated, one the Fulghum race and the other the Red Rust- 

 proof race. Further experiments have been carried out with these 

 races and the earlier results have been confirmed. Additional col- 

 lections of both U. Avenae and U. levis have been secured and 

 these have been tested on several varieties of oats. Evidence of 

 new i ices oi both species oi smut has been obtained. 



Physiologic Paces of Punt of Wheat 

 Bunt of wheat is a common and wide spread disease of this 

 crop, being co-extensive with its cultivation. There are two dis- 

 tinct species of smut (Tilletia lacvis and T. tritici) which cause 

 the disease. They are very similar in their life history, but are 

 readily distinguished by microscopic examination of their spores. 

 In our earlier work on varietal resistance a large number of dif- 

 ferent wheats, mainly winter types, have been tested in order to 

 determine their susceptibility or resistance. Definite collections of 

 both species of smut were used. By far the larger number of 

 common American winter types have proved to be susceptible. 



Our later studies have been mainly concerned with the problem 

 of the possible existence of physiologic races of these smuts and, 

 in earlier reports, announcements have been made regarding 

 definite evidence of the occurrence of such specialized races. Dur- 

 ing the past year a more extensive series of experiments was car- 

 ried out with a few winter wheat varieties. These were inocu- 

 lated and sown in the fall of i<p6 and harvested in the summer of 

 1927. The varieties were selected on the basis of their previous 

 behavior to the various collections of smut. 



Tweutv-oue different collections of T. lacvis were used, nine of 



