54 
periments all of the inoculated plants having been smutted. The 
method has proved particularly valuable in connection with the 
studies on inheritance of smut resistance, since it was necessary 
to make as certain as possible that all susceptible individuals were 
infected. In oat smut investigations, other methods have been 
developed and, during the past year, comparative experiments have 
been carried out on some of these. In these experiments we have 
used several different races of smut, as well as a number of oat 
varieties resistant or susceptible to them. Our method, in prac- 
tically every case, has given much better results than any other. 
Studies on Experimentally Produced Physiologic Races of the 
Oat Smuts 
Dr. L. Gordon Utter has continued his infection studies with 
collections of oat smut which resulted from hybridization between 
the loose and covered smuts of oats. In the previous report, a 
brief account of several selections, some of which may be new, 
distinct races of each smut, was given. The covered smut selec- 
tions were characterized by their infection of Gothland, a variety 
normally resistant to this smut but susceptible to the loose smut. 
Similarly, the loose smut selectious attacked Monarch, which or- 
dinarily is only susceptible to the covered smut. Additional ex- 
periments were carried out with 34 collections of smut, obtained 
from various oat varieties, which had been infected with the 
different selections. The reaction of these collections on several 
varieties of oats was determined and, on the basis of their behavior, 
at least eight distinct races of covered smut and seven of the loose 
smut were differentiated. Gothland continued to be susceptible 
to the covered smut collections, whereas Monarch showed a range 
from full resistance to susceptibility. The loose smut collections 
gave high infections on Monarch but Gothland was resistant to 
some and susceptible to the others. In both smuts, certain col- 
lections showed identical behavior and, therefore, were considered 
as a single race, while other collections were so striking in their 
reactions that they were tentatively classed as distinct races. Sev- 
eral collections from three new races of each smut, when tested 
on various oat varieties, were generally found to give infections 
so have 
a 
characteristic of the respective race. Several of the races a 
