52 
Physiologic Races of the Oat Smuts 
The extensive data obtained over a period of several years 
were assembled in order to determine the possible number of 
physiologic races differentiated. In the course of the experiments, 
approximately 200 species and varieties of oats have been inocu- 
lated with many of the smut collections which were secured from 
widely separated regions. We are especially indebted to Mr. T. R. 
Stanton, Senior Agronomist, Division of Cereal Crops and Dis- 
eases, Bureau of Plant Industry, Washington, D. C., who has 
supplied collections of smut from the important oat-growing re- 
gions of the United States. The problem has been to sift out 
the varieties of oats which were useful in separating possible races 
of smut. As the result of all the experiments, 29 distinct special- 
ized races of 
—" 
oose smut have been demonstrated on the basis of 
their reaction on 17 varieties of oats. In the same way, 14 special- 
ized races of covered smut of oats have been differentiated on 10 
varieties. Most of these specialized races are based on a single 
collection. In a few cases, however, several collections of smut 
seem to be identical. It 1s possible that further tests with addi- 
tional oat varieties might reveal one which would separate some 
of these other collections. A few races are capable of attacking 
a large number of oat varieties, while others appear to be quite 
narrowly limited in their capacity for infection. Of all the varie- 
ties of oats tested in the course of these experiments, only three 
have proved to be resistant to all of the races—Markton, Navarro 
and Victoria. 
Studies on the Methods of Inoculation of Oat Smuts 
Early in our studies on the inheritance of smut resistance in 
oats, special methods for the successful infection of susceptible 
varieties were worked out. The method as finally used over a 
period of years consisted of (@) removing the hulls from the 
grain, (b) inoculating the kernels with dry smut spores, and (c) 
germinating the seed in sand with a low moisture content, at a 
temperature of approximately 20° C. This procedure, using a 
variety of oat susceptible to the particular strain of smut, has 
regularly given very high percentages of infection, in many ex- 
