230 



MODIFICATION OF THE SOIL POPULATION 



the soil constituents. In peat bogs under natural conditions, 

 both fungi and aerobic bacteria are absent, especially a few inches 

 below the surface. The conditions are favorable only for the 

 growth of anaerobic bacteria. When peat bogs are drained, limed 

 in the case of acid peat bogs, and cultivated, and thus converted 

 into peat soils, they may profit considerably from inoculation with 

 fresh garden or field soil. One of the most important groups of 

 organisms thereby introduced is the group of nitrifying bacteria. 



Fig. 82. — Effect of inoculation upon growth of legumes. Left to right — 

 Soybeans; ten plants from an uninoculated plot, ten plants from an inocu- 

 lated plot. Pea vines; eight plants from an inoculated plot; eight plants 

 from an uninoculated plot (from Fred, Whiting and Hastings). 



When various leguminous plants are grown upon soil in which 

 the particular plants have never grown before, it is essential to 

 inoculate the soil with the specific types of the nodule-forming 

 bacteria, if a proper crop is to be secured and the best use made of 

 the particular plant on the given soil (Fig. 82). This is especially 

 true in the case of plants like alfalfa, soybeans, and cowpeas, when 

 introduced into regions in which these plants have never grown 

 before. Although the bacteria in general are quite widespread, 



