42 



THE MICROBE AND ITS ACTIVITIES 



the soil in separate communities, but are variously intermixed, so 

 that minute particles of soil contain many representatives of the 

 various groups of soil microbes. The reactions produced by 

 a single organism are far from simple, and the complexity of the 

 mixed population makes the reactions taking place in the soil 

 even more complicated. One set of conditions favors the devel- 

 opment of certain groups in preference to others. Many microbes 

 compete with one another for the available nutrients; many 

 complete one another, one using as food 

 the waste products of other organisms, 

 some depending for their nutrients upon 

 the activities of others. 



The sum total of the activities of the 

 various organisms is the liberation of 

 nutrients from the dead plant and animal 

 debris into forms available for the nutri- 

 tion of higher plants, as well as the 

 storage of some of the nutrients in the 

 microbial cells which contribute directly 

 or indirectly to the soil organic matter. 

 The environmental conditions modify 

 the nature of the soil population; the 

 nature of the organisms influences the 

 form in which the nutrients again be- 

 come available; the nature of these 

 nutrients influences the nature of the 

 plant vegetation which a given soil will 

 support. So intimately interwoven are these numerous reac- 

 tions that their products appear to be formed by a single 

 reaction from a single body. 



Fig. 35. — Beneficial soil 



nematode, Mononchus pa- 



pillatus (from Cobb). 



LITERATURE 



1. Greaves, J. E., and Greaves, E. O. Bacteria in relation to soil fertility. 



D. Van Nostrand Co. New York, 1925. 



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



McGraw-Hill Co. New York, 1923. 



3. LtJTMAN, B. F. Microbiology. McGraw-Hill Book Co., Inc. New York, 



1929. 



4. Marshall, C. E. Microbiology. P. Blakiston's Son and Co. Phila- 



delphia, 1921. 



