40 
ferences in the rate of growth and development of the oat plants. 
Hlowever, the varieties fully susceptible to a particular race of 
smut showed practically complete infection im every series, while 
the varieties which showed a moderate amount of infection gave 
no essential differences in the various experiments. 
These investigations have been supported in part by a grant 
from the Penrose Fund of the American Philosophical Society. 
Physiologic Races of the Oat Smuts 
A large number of collections of both loose and covered smuts 
were used to inoculate a series of varieties of oats, which belonged 
—_ 
to different recognized species. Most of the collections have 
already been grouped on the basis of their behavior, and the main 
object was to determine more particularly their capacity for in- 
fecting varieties of oats which have been developed in compara- 
tively recent years. 
In cooperation with Mr. TP. R. Stanton, Division of Cereal Crops 
and Diseases, Bureau of Plant Industry, Washington, D. C., ex- 
tensive data on the behavior of the collections of loose and covered 
smuts on red oat varieties were published. ‘two very distinct 
strains of loose smut have been differentiated, one occurring on 
the Fulghum group of red oats, and the other on the Red Rust- 
proof group. The Fulghum loose smut, while distinctly special- 
ized, occurs on a rather wide range of varieties. The RKed Rust- 
proof race is much more limited in its capacity for infection, 
Collections of covered smut have been made only on the Fulghum 
group of varieties. Of special interest is the fact that these 
collections of covered smut attack the hitherto recognized resistant 
Black Mesdag. Many additional varieties of oats belonging to 
the red oat group, as well as others, were specially tested with 
these various collections of smut, and the Red Rustproof race has 
continued to show very sharp limitation to a few varieties. 
Evidence has been obtained that there are distinct specialized 
subraces of both loose smut and covered smut on the Fulghum 
types. 
