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Cytological studies on the relation of the oat plant to the loose 
smut of oats have been carried out. Along another line, the study 
of a possible correlation in the growth rates of oats and of the 
covered smut in regard to infection was made. The investigations 
with sorghum smuts necessitated a detailed study of the effect of 
nutrients, moisture, and other environal factors on the percentage 
of infection in susceptible varieties of sorghum, in order to find 
the best conditions for obtaining the highest percentage of infec- 
tion, and environal factors which retarded seedling growth seemed 
to increase the percentage of infection; resistant varieties, however, 
showed no change in their response. 
The discovery of varieties fully resistant or susceptible, the 
working out of environal factors necessary to obtain complete 
infection of all individuals of susceptible varieties, the knowledge 
of the existence of physiologic races and the necessity of taking 
them into account, have made it possible to make progress on the 
study of the genetics of resistance. Many crosses have been made 
between oat varieties differing in their behavior to specific races 
of smut, and the resistance or susceptibility of second, third, and 
ater generations has been determined. In most cases the resis- 
tant quality is inherited on a simple one-factor basis. In others, 
_— 
however, the relation is much more complicated. Extensive 
studies on the inheritance of smut resistance in sorghums have 
also been carried out. 
The investigations in pathology have been conducted in cooper- 
ation with the Division of Cereal Crops and Diseases, United 
States Department of Agriculture, investigators in some of the 
State Experiment Stations, and practical breeders for the 1m- 
provement of cereal crops. 
In connection with the cultivation of the iris collection at the 
Garden, serious damage caused by the iris thrips was noted. Ex- 
tensive experiments were conducted in codperation with the Bu- 
reau of Entomology and Plant Quarantine in Washington, and 
effective methods of control were discovered. The insect could 
be killed by dipping the rhizomes in hot water for a given length 
of time. More convenient methods, however, were found in the 
use of derris and nicotine sulphate sprays. It was further found 
that fumigation with methyl bromide could be safely used. 
