QUESTIONS 465 



motile and possess flagella. Spore formation has not been observed. 

 The Azotobacter agilis is more lively motile than the Azotobacter 

 chroococcum. 



QUESTIONS. 



1. What is meant by the nitrogen cycle? Why is it necessary to preserve 

 animal and vegetable life on our planet? 



2. For what purpose do plants and animals need nitrogen? 



3. In what form can plants utilize nitrogen for their nitrogen metabolism? 



4. In what form do man and the lower animals mainly excrete the waste 

 nitrogen ? 



5. What is meant by a metabolic waste product? 



6. What becomes of urea excreted by animals? 



7. What is meant by decomposition of complex chemical compounds? 



8. Give some examples. 



9. What is the difference between putrefaction and decay? 

 10. Name some putrefactive bacteria? 



-11. What is meant by nitrifying bacteria? 



12. Describe some of their peculiar biologic properties. 



13. Under what conditions will nitrification, brought about by bacteria, go 

 on in the soil? 



14. What microorganisms have the power to decompose urea? Name some 

 of the most important ones. 



15. Describe the Micrococcus urese. 



16. Describe the Micrococcus urese liquefaciens. 



17. Describe the Urobacillus Pasteuri. 



18. What is the difference in action between the two groups of nitrifying 

 bacteria? 



19. Describe the different species of nitrosomas. 



20. Describe a species of nitrosococcus. 



21. In what fluid are they best examined microscopically? 



22. Describe the morphology and the growth of nitrobacteria. 



23. What is meant by denitrification ? 



24. Name some bacteria which in the absence of free oxygen can act as 

 denitrifiers. 



25. Under what circumstances can these bacteria produce great loss of nitrates 

 in improper fertilization of the soil? 



26. What plants have the power to utilize nitrogen from the atmosphere for 

 their metabolism? 



27. What are the root tubercles of leguminosae? 



28. What is the name of the bacillus contained in the root tubercles? What 

 is its physiologic function ? 



29. What is the best culture medium for this bacillus? How can we obtain 

 pure cultures of the Bacillus radicicola? 



30. Describe the morphology of this bacillus. 



31. Discuss the question whether or not there are a number of species of the 

 Bacillus radicicola. 



32. Describe how this organism penetrates into the root hair and what changes 

 it produces. 



33. What is meant by bacterioid tissue? Describe it in detail. 



34. Discuss the nitrogen content of root tubercles at various periods of the 

 plant's life. 



35. What is meant by green manuring? What is its object and effect? 



36. Name some bacteria which are nitrogen fixers but not in symbiotic com- 

 munity with higher plants. 



37. Describe the morphologic and biologic properties of Clostridium Pasteuri- 

 anum. 



38. What kind of organism is azotobacter? 



30 



