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areas in England and Europe and the eastern United States, 

 formerly fertile, are now unproductive because the nitrogen in the 

 soil has been exhausted. 



But now man has captured a tiny germ invisible to the naked 

 eye, which can take from the boundless store of nitrogen he has 

 coveted and put it into the earth for him. 



Ever since the time of Pliny, farmers have noticed that after a 

 crop of peas, alfalfa or any of the leguminous plants, a heavier 

 yield of wheat can be obtained ; thus has arisen the old profitable 

 rule of rotation of crops. 



But the reason certain plants enrich the ground while others 

 exhaust it, remained a mystery until an enquiring German discovered 

 some years ago that peas, beans, etc., obtained their nitrogen food 

 not from the nitrates in the soil, but from the free supply of the air. 

 He also discovered that these plants absorbed much more nitrogen 

 than they could use and left the surplus in the soil. That is, 

 beans, peas, alfalfa, clover, put back into the mother earth what 

 corn and wheat and grain remove. The manner in which they do 

 this is unique and another instance of the marvellous and mysle- 

 rious laws by which the balance of nature is maintained. 



If one digs up a healthy bean or clover plant and examine the 

 roots, he will see a number of rounded bulbs, called nodules or 

 tubercle, on the roots. At first sight he might imagine that the 

 plant had a lot of sores over it, that it was diseased, or had been 

 bitten by worms or insects. All legumes have these nodules or 

 tubercles, varying in size from a pinhead to clusters as large as a 

 good-sized potato. Scientists noticed that plants with good-sized 

 nodules flourished, while plants without nodules or with very small 

 ones looked starved and withered, and they concluded that the 

 nodules must have something to do with the vigour of the plants. 

 On dissecting a bulb and examining it under a microscope, it was 

 found to be packed with bacteria. Further examination showed 

 that it, and all nodules, consist of millions of bacteria and that 

 these bacteria were incessantly absorbing free nitrogen from the 

 air and converting it into forms suitable for the plant's digestion. 



For want of a better term we will call the germs nitrogen-fixing 

 bacteria. 



Careful examination of the earth showed that all soil where 

 legumes grow contain these nitrogen-fixing bacteria, in greater or 

 less quantities ; that these organisms settle on the plants and form 

 the colonies or tubercles on the roots. If the soil contain none of 

 these organisms to settle on the roots, the legumes will not grow 

 at all. Each tubercle acts as a feeder to the plant. The more 

 numerous and larger the tubercles, the more prosperous is the 

 plant. One might thus define a tubercle as a little factory 

 where millions of tireless infinitesimal workers are separating the 

 nitrogen in the air and converting it into plant-food. A celebrated 

 German, Professor Nobbe of Tharandt, realized that if he could 

 put into barren ground some of these organisms, or if he could 



