86 ALFALFA FARMING IN AMERICA. 
the soil in the way of nourishment, but what they 
find is not enough to satisfy the ambitions of the 
alfalfa plant. Therefore it calls to its aid a host of 
tiny slaves, the bacteria. All clovers have useful 
bacteria that live upon their roots and gather nitro- 
gen from the air. Then when the bacteria die the 
nitrogen is taken up by the plant and made into its 
tissue, into its leaves, stems and seeds. These bac- 
teria live primarily for themselves, fastening to the 
little root hairs. Soon these little root hairs push 
out tissue and enclose the bacteria in fleshy ex- 
crescences shaped like little grapes or seeds. These 
excrescences we call tubercles or nodules. They are 
as large as clover seed or larger, or smaller. They 
occur singly or in masses. Sometimes soils seem 
naturally full of these bacteria so that as soon as 
the alfalfa is sown they come on the roots. When 
this is true the alfalfa starts off with great vigor 
from the beginning and endures in thrift nearly al- 
ways. At other times soils are found to be barren 
of these bacteria and no nodules form upon the roots. 
Then the alfalfa seems half starved, weak, yellow, 
sickly. 
Where Bacteria Thrive——In some soils it is im- 
possible to establish these bacteria by artificial trans- 
plantation or otherwise. When this is true alfalfa 
will never thrive. It may live for a time by aid of 
manures and cultivation, but it is not thrifty and it 
finally suecumbs. It cannot withstand the onslaughts 
of weeds without the aid of these bacteria feeding its 
roots. They get their nitrogen and thus much of 
