8 BULLETIN 1058, 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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