THE SOIL AS A CULTURE MEDIUM 



623 



ture content by filamentous fungi and aerobic bacteria ; at a low mois- 

 ture content, by filamentous fungi and actinomyces; when the soil is 

 saturated with water, anaerobic bacteria are largely concerned with 

 the decomposition of the cellulose. When sugar is added to the soil 

 and the development of microorganisms is followed by direct micro- 

 scopic examination, Azotobacter is found to develop under aerobic 

 and Bac. amylobacter under anaerobic conditions. The latter condition 



TABLE 64 

 Influence of moisture upon the formation of ammonia and nitrate [from horn meal) 



in different soils 



may be reached below the surface even when the moisture content of 

 the soil is only 40 per cent of saturation. 9 



The influence of moisture upon the activities of bacteria is due to two 

 factors: 10 (1) penetration of atmospheric oxygen through the medium; 



9 Winogradsky, 1924 (p. 542). 



10 Rahn, O. Die Bakterientatigkeit im Boden als Funktion der Nahrungs- 

 konzentration und der unloslichen organischen Substanz. Centrbl. Bakt. II, 

 38: 484-494. 1913; Bacterial activity in soil as a function of the grain-size and 

 moisture content. Mich. Agr. Exp. Sta. Tech. Bui. 16. 1912. 



