62 



SUMMARY 



1. Vanillin, cmnarin, pyridine and quinoline when 

 added separately to the soil used in these experiments 

 at a concentration of approximately 1000 parts per 

 million of air dry soil produce a great temporary in- 

 crease in the number of bacteria which will develop 

 on Brown's albumen agar. 



2. In the case of vanillin and quinoline it is shown 

 that this increase in numbers is preceded by a decrease. 



3. The number of Actinomyces colonies in the soils 

 treated with cumarin, vanillin and quinoline decreases, 

 reaching a minimum roughly corresponding with the 

 maximum in bacterial numbers. 



4. Steam sterilizing of the soil used in these experi- 

 ments produces material toxic to the growth of wheat 

 plants. Soil microorganisms destroy the toxicity of 

 the steamed soil under the conditions of the experiment 

 reported. 



5. The effect on the growth of wheat of vanillin, 

 cumarin, pyridine and quinoline in sterile soil and in 

 soil which had been sterilized, reinoculated and in- 

 cubated was compared. In the inoculated soil the toxi- 

 city of the four compounds largely disappears. It per- 

 sists in the sterile soil. 



6. Specific bacteria were isolated from the soils used 

 which utilize cumarin, vanillin and pyridine as food 

 sources. 



7. The bacterium feeding on vanillin will in pure 

 culture destroy the toxicity of vanillin to wheat. 



8. The bacterium feeding on cumarin will in pure 

 culture destroy the toxicity of cumarin to wheat. 



9. The increase in the numbers of bacteria in the 

 soils treated with the four compounds mentioned and 

 the disappearance of the toxicity of these substances 

 in inoculated soil is therefore believed to be due to the 

 fact that they serve as favorable food sources to definite 

 species of bacteria. 



LITERATURE CITED 



1. Buddin, W. 



1914. Partial sterilization of soil by volatile and 

 non-volatile antiseptics. In Jour. Agr. Sci. V. 6, pt. 

 4, p. 410-451, 4 figs. 



2. Brown, P. E. 



1913. Methods for bacteriological investigations of 



soils. Iowa Agr. Exp. Sia. Research Bui. il, p. 381- 

 407. 



3. Davidson, J. 



1915. A comparative study of the effect of cumarin 



