4 BULLETIN 1053, U. S. DEPARTMENT OF AGRICULTURE. 
It is quite evident, however, that considerable sterility occurs on 
oat panicles which have not come in contact with diseased leaves or 
sheaths, and even in fields where there has been little or no bacterial 
blight; also there is evidence that in years of severe bacterial blight 
early in the season the yield per acre has not been reduced, but some- 
times has been greater than when there was less blight. 
In order to learn more about the relationship of the halo blight 
to the sterility of oats the observations and experiments described 
in the following pages were made. 
EXPERIMENTS OF 1918. 
During the season of 1918, 11 varieties of oats were used for 
inoculation experiments. In each variety bundles containing about 
a dozen plants were sprayed with water suspensions of the halo- 
blight organism and covered with glassine bags for two or three days. 
One bundle was sprayed without being injured in any way and another 
after the plants had been drawn between the fingers to rub off the 
bloom. The plants of a third bundle of each variety were injured 
by needle pricks or were cut with a scalpel before spraying. Check 
bundles of each variety, injured and uninjured, were sprayed with 
sterile water and also covered with bags. In some cases water 
suspensions of the organism were sprayed into unopened sheaths 
and sterile water into similar plants as checks. (Pis. I to IV.) 
In most of the varieties the sheaths were about ready to open or 
were already partly open. In Wisconsin Pedigree 7 the heads were 
entirely out of the sheaths and were inoculated to learn whether 
or not the spikelets themselves were susceptible to infection with the 
halo-blight organism and what the effect of infection would be. 
In the oat panicle the uppermost spikelets develop first and at the 
time when the sheath is about ready to open are usually fully grown, 
while those at the base are still only partly developed. The difference 
in the stage of development of the spikelets on the panicle influences, 
of course, the results of the experiments where inoculations are made 
upon panicles about to emerge from the sheath. The almost fully 
developed spikelets at the top are less influenced by the inoculum 
than the partly developed ones at the base. 
When these inoculated and check plants were mature and were 
collected for recording the results, a bundle of untreated plants of 
each variety was also collected in order to compare the proportion 
of sterility with that of treated plants. The results of this set of 
inoculations, together with the amount of sterility found on untreated 
plants, are shown in Table I, and a brief summary of the same is 
presented in Table II. 
