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 succumbs. It cannot withstand the onslaughts 

 of weeds without the aid of these bacteria feeding its 

 roots. They get their nitrogen and thus much bi 



