320 SlRUCTURE AND LIFE HISTORIES 



the nitrogen-fixing bacteria this process would continue 

 until all complex nitrogenous compounds were reduced 

 to ammonia or free nitrogen. All life would then cease, 

 because green plants, upon which animal life is de- 

 pendent, are unable to live without nitrogen, and they 

 cannot utilize it in the form of ammonia nor of free 

 nitrogen. Without chlorophyll and the nitrogen- fixing 

 bacteria, therefore, all life would cease. Thus it is that 

 life and death, health and disease, wealth and poverty, 

 misery and happiness, are dependent upon the activity 

 of tiny plants, too small to be seen, except under the 

 highest powers of the microscope. 



