SECTION XXIX. LEGUMES AND 

 INOCULATION 



IN former times learned men thought that mankind 

 would finally starve to death because there is not enough 

 nitrogen in the ground to produce food sufficient to feed 

 the growing population of the world. There is no longer 

 any fear of this, for it is known that certain plants called 

 legumes can make use of the limitless amounts of nitrogen 

 in the air. There are about 36,000 tons of this nitrogen 

 gas in the air above every acre. Yet cotton, corn, wheat, 

 and most plants cannot use a pound of this nitrogen gas 

 until legumes have changed it into fertilizer nitrogen. Any 

 of the legumes, for example, the cowpea or clover, by the 

 aid of the tubercles on its roots (Fig. 112), can grow on 

 ground where cotton, corn, or wheat would starve for want 

 of nitrogen. Not only do legumes get from the air enough 

 nitrogen to enable them to make luxuriant growth on a 

 poor field, but they also enrich the soil with a part of this 

 nitrogen. When the roots and fallen leaves decay, the 

 nitrogen in them is added to the soil. Still more is added 

 if the stems and leaves, as well as the roots, are left on the 

 field where the plants grew. That crops often grow much 

 larger after a legume is shown in Fig. 1 10. 



Each germ grows only on the kind of plant to which it 

 is accustomed. Every tubercle on the roots of legumes is 



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