16 



CONTRIBUTING CAUSE OF INJURY TO SEED-CORN BY REPELLENTS 



That the cause was indeed local is indicated by the fact that in a 

 prolonged trip through central Illinois, made during the summer of 

 1907, for an inquiry concerning the use of lemon oil and its results, 

 Mr. Davis found a general complaint of injury to the seed in the 

 vicinity of Galesburg, arid especially between Knoxville and De Long, 

 in all of the territory covered by his trip the lemon-oil treatment had 

 been more or less used in practically all localities except in Christian 

 county, and there was commonly no report of injury to the seed, the 

 main complaint of the farmers being the fact that they found no dif- 

 ference in respect to thrift and stand between treated and untreated 

 corn. 



What the local cause of injury probably was in these various cases 

 is shown by the record of rainfall at Bloomington, given on a preced- 

 ing page, taken in connection with the proof contained in Dr. Whit- 

 ten's studies, already referred to, that kerosene and other volatile oils 

 are injurious to seed-corn in proportion to the amount of moisture in 

 the ground during the planting and germinating period. In discussing 

 his own exi)eriments. Dr. Whitten says : 



"When the amount of water in the soil was reduced from 30% 

 saturation to 25% saturation, the per cent, of germination was increased 

 and the growth of the seedlings was more nearl\- normal ; but when the 

 water content of the soil was increased to 50 or 75% saturation, the 

 per cent, of germination was markedly decreased and the subsequent 

 growth of many of the seedlings abnormal." Again he says: "It is 

 evident that within certain limits the seedlings are not injured by the 

 oil present at the time of planting, provided growth is initiated in the 

 presence of a minimum amount of water. The small quantities of 

 kerosene are toxic in proportion to the increase of the moisture con- 

 tent of the soil. In the 50 and l^'^c saturated soils the dormant period 

 of the grain is always less than 36 hours, while in the 25% saturation 

 the time is extended to approximately five days. This increase of time 

 afifords the seedling an opportunity to dispose of the oils mucli more 

 slowly, and it does so without injurious effects."^ 



The Bloomington rainfall of nearly two and three-quarters inches 

 distributed over seven days and including the planting period of the 

 Normal field, must have kept the ground unusually moist from the be- 

 ginning, and is a sufficient explanation of the injury to seed-corn in 

 that field. Unfortunately, I can obtain no weather record of a place 



'Bull. 111. State Lab. Nat. Hist., Vol. X, Art. V, pp. 266-267, 268. 



