DECOMPOSITION OF NON-NITROGENOUS ORGANIC MATTER 447 



no dark colored substances are formed directly from the decomposition 

 of celluloses in the soil, the sources of "humus" are to be looked for 

 in the other plant constituents besides the celluloses (p. 691). How- 

 ever, indirectly cellulose may contribute to the soil organic matter or 

 "humus", due to the fact that it is a readily available source of energy 

 and is decomposed in aerated soils largely through the activities of 

 fungi and bacteria, resulting in the synthesis of an extensive mi- 

 crobial protoplasm. 59 



Although celluloses cannot be used directly as sources of energy for 

 nitrogen-fixing bacteria, they may form products which are available 

 sources of energy for these organisms. Beijerinck 60 found that a 

 medium consisting of two parts of paper, two parts of chalk and 0.05 

 per cent K2HPO4 in 100 cc. of tap water was a favorable medium for 

 nitrogen-fixation. At 25° to 30°, there developed chiefly the hydrogen- 

 forming organism together with Bad. radiobacter and Azotobacter. For 

 every gram of cellulose decomposed, 8 to 9 mgm. of nitrogen were 

 fixed. Bac. amylobacter* 1 and Azotobacter 62 are unable to attack cellu- 

 lose in pure culture. Only in mixture with cellulose decomposing 

 organisms, are they able to fix nitrogen, at the expense of the cel- 

 lobiose, the glucose or the fatty acids formed from the decomposition of 

 the cellulose. In a mixture of the methane-forming organism and 

 Clostridium americanum, Pringsheim 61 obtained 12.1 mgm. nitrogen fixed 

 for 1 gram of cellulose decomposed. The methane bacterium produced 

 10 grams fatty acid out of 20 grams cellulose ; but in the presence of nitro- 

 gen-fixing organisms, only 0.064 gram fatty acid accumulated. Azoto- 

 bacter fixed 4.5 mgm. of nitrogen out of 1 gram of cellulose, in sym- 

 biosis with the methane organism; this is probably due to the fact that 

 Azotobacter does not thrive well under semi-anaerobic conditions. 



"Waksman, S. A. Soil Sci., 22: 123-162, 221-232, 323-333, 395-406. 1926. 



60 Beijerinck, M. W. L'influence des microbes sur la fertilite du sol et la 

 croissance des vegetaux supe^rieurs. Arch. Neerland. Sci. Ex. Nat. Ser. II, 

 9: 8-36. 1904. 



61 Pringsheim, H. Ueber die Verwendung von Cellulose als Energiequelle 

 zur Assimilation des Luftstickstoffs. Centrbl. Bakt. II, 23: 300-304. 1909; 

 26: 222-227. 1910. Die Beziehungen der Zellulosezersetzung zum Stickstoff- 

 gehalt in der Natur. Mitt. deut. landw. Gesell., 1912, 1913, p. 26, 43 (Centrbl. 

 Bakt. II, 37: 111. 1913). 



62 Koch, A., and Seydel, S. tlber die Verwertung der Zellobiose als Ener- 

 giequelle bei der Stickstoffbindung durch Azotobacter. Centrbl. Bakt. II, 

 31: 567-577. 1911. 



