8 BULLETIN 1053, U. S. DEPARTMENT OF AGRICULTURE. 
show the greatest amount of sterility. By spraying plants with 
sterile water or water suspensions of bacteria and covering them 
for two or three days, the amount of sterility can be greatly increased. 
Although abundant halo lesions result from spraying with bacterial 
suspensions, the consequent sterility is only slightly, if any, greater 
in amount than that induced by sterile water. 
It seems probable that rains falling about the time the oat sheaths 
are ready to open may have the same effect as the sterile water used 
in the experiments recorded here and that most of the sterility 
observed in oat fields is not the result of the halo-blight organism 
but of too much moisture about developing panicles. 
The striking variations in percentages of sterility in different 
panicles of the same bundle (Table I, Wis. Ped. 14, bundles 1 to 6) and 
the high percentages of sterility in all the panicles of a few bundles 
(Table I, Wis. No. 25, bundles 4 and 5, and Table I, Wis. No. 22, 
bundles 3 and 4, 1918; also Table IV, bundles 2, 3, and 4, 1920) would 
seem to point to the condition of the oat flowers at the time of rain 
or spraying as a controlling factor in the amount of sterility. If, how- 
ever, the variations in the amounts of sterility in different varieties 
should prove constant from year to year the varieties found to be sus- 
ceptible could be discarded and hardier ones grown. Records for 
several years from parallel plats of varieties which have shown differ- 
ent amounts* of sterility in one season might give interesting and 
practical results. 
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