226 ALFALFA FARMING IN AMERICA. 
enormous amounts in the air. Nearly 80% of the 
air is pure nitrogen. Why can not the leaves take 
it directly in as they do their carbon from the air? 
That we do not know, but they can not doit. Plants 
will starve and perish for nitrogen with their leaves 
bathed in that substance, with their roots surround- 
ed with it as well, for in all porous soils there is 
much air. 
About Bacteria—Bacteria do the work. Bacteria 
are very minute plants, sometimes almost like ani- 
mals in having some power of motion. Yeast is a 
bacteria. They are intensely minute. It would take 
5,200 of them, placed in a row, to be an inch long. 
Twenty-seven million could be on a square inch of 
space. A farmer can not ever hope to see one; it 
takes a powerful microscope to show one, yet any 
farmer can see the work they do. 
It is thought that there is really only one sort of 
bacteria for all the clovers, but that habit has divided 
them into varieties, similar yet unable to live on the 
same plants. Thus there are the red clover bacteria, 
the cowpea bacteria, the alfalfa bacteria, and many 
more. Some bacteria live on several different plants, 
just as the alfalfa bacteria thrive on melilotus, al- 
falfa and burr clover. 
These bacteria when they touch a tiny rootlet of 
alfalfa have power to enter it and abide there. They 
increase there and swarm in incredible numbers. 
They are really parasites upon the plant, most like- 
ly. The plant attacked puts out a protective cover- 
ing, thus forming a swelling nodule on the little 
