THE COW PEA. 39 



tankage contain nitrogen, certain chemical changes must 

 take place before this nitrogen can feed the plant. In 

 the nitrate of soda these changes have already taken 

 place, hence the nitrate is at once effectual. In like 

 manner, atmospheric nitrogen is not available to most 

 plants, but the cow pea is capable of making it over and 

 combining it so that it is. Those who have seen the 

 pigeon feed its young have a clear illustration of the way 

 the cow pea plant feeds other plants. The mother pigeon 

 gathers, swallows, and partly digests the food, and then 

 brings it up to her mouth as "pigeon milk" and feeds it to 

 her young. This subject is explained at some length to 

 show why the cow pea on poor land gives such wonderful 

 results with only the addition of the mineral elements, pot- 

 ash and phosphoric acid. The value of most manures 

 depends largely upon their rapidity of decay, to bring their 

 nitrogen to plant support. The cow pea vine decays 

 quickly, and is probably the "quickest" in its manurial 

 effects of any green manuring crop. 



An examination of the roots of a healthy cow pea, 

 or other legume, discloses many little bunches, enlarge- 

 ments, "nodules" or "tubercles," varying in size from 

 that of a small pinhead to a pea. These have about the 

 consistency and much the appearance of very small pota- 

 toes, but an examination with the microscope shows that 

 they contain vast numbers of livings things, actually 

 myriads of minute living organisms, scientifically named 

 bacteria. These bacteria draw the small mineral part of 



