34 THE COW PEA. 



becomes available and the plant quickly responds to its 

 use. The reason for this is, though the meal, the blood 

 and the 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 which explains why 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. Thevalueof 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 "quicke»«" 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 ver}- small pota- 

 toes, but an examination with the niicroscope shows that 

 they contain vast numbers of living things, actually myriads 



