LITERATURE 241 



and more numerous individuals where considerable amounts of 

 organic substances reach the soil in such forms as plant residues, 

 animal manures, or commerical fertilizers. Certain inorganic 

 substances also accelerate microbial development. It is thus 

 possible to modify the population and consequently its acti\aty 

 by systematically regulating the cultural treatments. In some 

 special cases it is desirable to modify the population to an extreme 

 degree by the addition of certain antiseptics or by heating the soil. 

 Likewise, soil inoculation is effective where certain leguminous 

 plants are to be grown. 



It is by reason of the fact that the soil population is more active 

 in fertile soil that microbiological methods are available for esti- 

 mating soil fertility. Information as to whether or not the organ- 

 isms are relatively numerous or scant, as well as information con- 

 cerning what treatments improve their development, is very useful 

 in judging soils and determining requirements for their improve- 

 ment. 



LITERATURE 



1. Fred, E. B., Whiting, A. L., and Hastings, E. G. Root nodule bacteria 



of Leguminosae. Wisconsin Agr. Exper. Station Research Bulletin 

 72, 1926, pp. 1-43. 



2. LiPMAN, J. G. Bacteria in relation to country life. Chapters 23, 27-32. 



The Macmillan Co. New York, 1921. 



3. LoHNis, F., and Fred, E. B. Textbook of agricultural bacteriology. 



Chapter 13. McGraw-Hill Book Co., Inc. New York, 1923. 



4. Russell, E. J. Soil conditions and plant growth. Chapter 6. Long- 



mans, Green & Co. London, 1927. 



5. Waksman, S. a. Principles of soil microbiology. Chapters 27, 28, and 31 



The Williama & Wilkins Co. Baltimore, 1927. 



