NON-SYMBIOTIC FIXATION OF NITROGEN 255 



11. Is B. radiobacter present? What part does it play 

 in the fixation of nitrogen? 



12. Make several agar slant pure cultures of B. radio- 

 bacter. 



13. Study the morphology and the cultural character- 

 istics of this organism. 



14. Inoculate a small flask of the mannit solution with 

 a pure culture of the newly isolated organism. 



15. How does this organism compare, morphologically, 

 culturally, etc., with Ps. radicicolaf With the Azotobacter? 



What part in the nitrogen cycle does the Azotobacter play? 



What practices of the farmer favor the development of 

 the Azotobacterf In what way? What soil conditions are 

 favorable to the Azotobacter species? Are these condi- 

 tions favorable to other bacteria? To plants? 



Diseased spots in soil are said to be caused by an 

 excessive nitrogen fixation and nitrification, e.g., the niter 

 spots in Colorado soils. 



16. State your results in full and draw conclusions. 

 Point out the practical applications of the above. 



REFERENCES 



MARSHALL: Microbiology, pp. 98-99, 230-231, 248, 250, 266, 270-273, 



286, 288, 291. 

 LIPMAN and BROWN: Laboratory Guide in Soil Microbiology, pp. 



43-45. 

 HOFFMAN, C., and HAMMER, B. W.: Some Factors Concerned in the 



Fixation of Nitrogen by Azotobacter. Research Bui. No. 12, 



Univ. of Wis. (1910). 

 JONES, DAN II.: A Morphological and Cultural Study of Some 



Azotobacter. Cent. f. Bakt. II Abt., Bd. 38 (1913), pp. 13-25, 



5 plates. 

 Further Studies with Some Azotobacter. Cent, f . Bakt. II Abt., 



Bd. 42, pp. 68-69. 

 LOHNIS: Laboratory Methods in Agricultural Bacteriology, pp. 40, 



113-114, 127. 

 HEADDEN, W. P. : The Fixation of Nitrogen in Colorado Soils. Buls. 



178, 186, Colorado Agr. Expt. Sta. 



