Cultivated-Plant Study 



653 



upon their roots the little swellings, or nodules, which are the houses in 

 which the beneficent bacteria grow. 



If we pull up or dig out the roots of alfalfa, or of the 

 true clovers or vetches, we find upon the rootlets little 

 swellings which are called nodules, or root-tubercles. 

 Although these tubercles look so uninteresting, no fairy 

 story was ever more wonderful than is theirs. They are, 

 in fact, the home of the clover brownies, which help the 

 plants to do their work. Each nodule is a nestful of liv- 

 ing beings, so small that it would take twenty-five 

 thousand of them end to end to reach an inch; therefore, 

 even a little swelling can hold many of these minute 

 organisms, which are called bacteria. For many years 

 people thought that these swellings were injurious to the 

 roots of the clover, but now we know that the bacteria 

 which live in them are simply underground partners of 

 these plants. The clover roots give the bacteria homes 

 and place to grow, and in return these are able to extract 

 a very valuable chemical fertilizer from the air, and to 

 change its form so that the clovers can absorb it. The 

 name of this substance is nitrogen, and it makes up more 

 than three-fourths of the air we breathe. Other plants 

 are unable to take the nitrogen from the air and use it for 

 food, but these little bacteria extract it from the air which 

 fills every little space between every two grains of soil and 

 then change it to a form which the clovers can use. 

 After the clover crop is harvested, the roots remain in the 

 ground, their little storehouses filled with this precious 

 substance, and the soil falls heir to it. 



Nitrogen in the form of commercial fertilizer is the 

 most expensive which the farmer has to buy. So when 

 he plants clover or alfalfa on his land, he is bringing to the 

 soil this expensive element of plant growth, and it costs 

 him nothing. This is why a good farmer practices the 

 rotation of crops and puts clover upon his land every three or four years. 



Alfalfa showing 

 root-tubercles. 



Yellow or hop clover. 



Buffalo clover. Rabbit-foot or pussy clover. 



