562 



PRINCIPLES OF SOIL MICROBIOLOGY 



firmation; this is especially important since the bulk of the energy- 

 material commonly added to the soil consists of celluloses and pen- 

 tosans. It is claimed that the latter can be used as a source of energy 

 by nitrogen-fixing bacteria. 8 



Table 55 contains a summary of the results obtained by different 

 investigators concerning the relative availability of different sources of 

 energy for nitrogen fixation; the results are rather variable and point to 

 the unreliability of such criteria, which are subject to numerous influ- 

 ences. By using different periods of incubation, media of different 

 composition and different soils for inoculation (difference in mixed flora) , 

 a different series of results would be obtained. 



As to the availability of natural organic materials as sources of energy 

 for nitrogen fixing organisms, table 56 shows the amounts of nitrogen 

 fixed for 100 grams of carbon by Az. chroococcum, as determined by 



TABLE 56 



Nitrogen fixed by Az. chroococcum for 100 grams of carbon 



Dvorak. 9 He used a medium containing 1 gram K 2 HP0 4 and 1 gram 

 CaC03 in 1 liter of tap water; 10 grams of organic matter and 250 cc. of 

 medium were placed in liter flasks, which were then sterilized and 

 inoculated. 

 The favorable action of the last four substances preceding glucose is 



Bottomley, W. B. The assimilation of nitrogen by certain nitrogen-fixing bac- 

 teria in the soil. Proc. Roy. Soc. B., 82: 627-629. 1910; 85: 466. 1912; Koch, 

 A. Uber Luftstickstoffbindung im Boden mit Hilfe von Zellulose als Energie- 

 materia'. Centrbl. Bakt. II, 27: 1-7. 1910; 31: 567-570. 1912; Stoklasa, J. 

 Beitrag zur Kenntnis der chemischen Vorgange bei der Assimilation des elemen- 

 taren StickstofTs durch Azotobacter und Radiobacter. Centrbl. Bakt., II, 21: 

 4S4-509, 620-632. 1908. 



8 Stranak, Fr. Zur Assimilation des LuftstickstofTes durch im Boden freileb- 

 enden Mikroorganismen. Zeitschr. Zuckerind. B>hmen 33: 599. 1909; (Centrbl. 

 Bakt. II, 25: 320. 1909). 



• Dvorak, 1912 (p. 428). 



