6 
The two species also may be distinguished by their pathological 
effects upon the host. The loose smut causes a very complete 
destruction of the kernel and inclosing glumes. Soon after the oat 
panicle emerges from the boot the black, dusty spores with the rem- 
nants of the host tissues are disseminated, leaving the naked, slightly 
branched rachis. The infected heads in the crop appear before or 
with the normal heads. The covered, or hidden, smut also causes 
the destruction of the kernel, but the protecting glumes are less 
involved, remaining more or less intact and partially concealing 
the smut spore masses. There is very little dissemination of the 
spores in the field, so that the infected panicles and their spores are 
harvested with the sound grain. The smutted heads appear simul- 
taneously with or usually a little later than the normal heads (PI. I) . 
The life histories of the two species are in general quite similar. 
Both parasites penetrate the very young seedlings of the host. The 
mycelium grows in the embryonic host tissues, and the spores are 
produced in the ovaries and adjacent structures. 
It is probable that the loose smut is disseminated very largely by 
spores which reach the kernel during its development in the field. 
Jensen (8) has emphasized the possible importance of the spores 
present between the kernel and the protecting husks. Zade (22) has 
recently shown that the spores of the loose smut may germinate in 
the developing flower and form a rudimentary mycelium in the outer 
tissues of the kernel or in the adjacent glumes. This type of flower 
infection, however, is very different from t}^pical flower infection as 
found in Ustilago tritici and U. nuda. Whatever may be its im- 
portance in the development of smut or whatever may be the im- 
portance of spores inclosed by the husks, it is evident from numerous 
inoculation experiments that high percentages of infection of oats 
may be obtained by dusting the dry spores on the outside of the 
grain. 
The dissemination of the spores of the covered smut takes place 
very largely in harvesting, threshing, and similar operations. The 
spores are separated from the inclosing tissues and scattered over 
the adjacent sound kernels. 
FIELD EXPERIMENTS 
EXPERIMENTAL PROCEDURE AND RESULTS 
The investigations of the senior writer on the varietal resistance 
and susceptibility of oats to loose and covered smuts have been con- 
tinued in the United States Department of Agriculture in cooperation 
with a number of State agricultural experiment stations and later at 
the Brooklyn Botanic Garden, Brooklyn, N. Y. The experiments 
under way at the Missouri Agricultural Experiment Station at 
Columbia were continued. Extensive sowings were made at Aber- 
deen, Idaho, in cooperation with the Idaho Agricultural Experiment 
Station in 1919 and 1920. In cooperation with the Iowa Agricul- 
tural Experiment Station, similar studies were carried on at Ames 
in 1919 and 1920. Sowings also were made at the Kansas Agricul- 
tural Kxpcriment Station at Manhattan in 1920 and at the Washing- 
ton Agricultural Experiment Station at Pullman in the same year. 
At Pullman the seed sown was inoculated with the covered smut 
( f'sf ilago levis) only. At all the other stations both smuts were 
used for inoculating the seed. 
