40 



PRINCIPLES OF SOIL MICROBIOLOGY 



Loam soils were found 90 to contain a higher number of actinomyces than 

 other soils, sandy soils coming last; a proportionate increase of these 

 organisms was found in the fall (27 to 35 per cent) over the spring (18 to 

 23 per cent), but no reduction was observed in the winter. Cultivation 

 of the soil effected a decrease in the numbers of actinomyces. These 

 organisms are also found abundantly in forest soils (24 to 27 per cent 

 of the flora) and on the roots of different plants, particularly grass and 

 legume roots, the upper cell layers of which died down. 



The soil microflora developing on the plate may consist of as many as 

 40 per cent of actinomyces; the total number of these organisms was 

 found to be as high as 12 to 14 millions per gram of soil. 91,92 Sod soils 

 contain larger numbers of actinomyces than cultivated soils and it was 



TABLE 6 



Bacteria and actinomyces at various depths 



Average of three New Jersey soils 



suggested, therefore, that they may play an active part in the decom- 

 position of organic matter in the soil. 93 The numbers of actinomyces 

 decrease regularly with depth, but they increase in proportion to the 

 other microorganisms, so that at a depth of 30 inches they form 65. G 

 per cent of the total microbial flora developing on the agar plate. 94 



90 Fousek, A. tlber die Rolle der Streptotricheen im Boden. Mitt. Landw. 

 Lehrkan. K. K. Hochschule f. Bodenk. Wien, 1: 217-244. 1913. 



91 Conn, H. J. Distribution of bacteria in various 'soil types. Jour. Amer. 

 Soc. Agron. 5: 218-221. 1913. 



92 Krainsky, A. Die Aktinomyceten und ihre Bedeutung in der Natur. 

 Centrbl. Bakt. II, 41: 649-688. 1914. 



93 Conn, H. J. A possible function of actinomycetes in soil. Jour. Bact. 1: 

 197-207. 1916; N. Y. State Agr. Exp. Sta. Tech. Bui. 60. 



94 Waksman, S. A., and Curtis, R. E. The actinomyces of the soil. Soil 

 Sci. 1: 99-134. 1916. 



