202 Agricultural Bacteriology. 



scope, it will be seen to be filled with innumerable bac- 

 teria that move about in the water in which the contents, 

 of the nodule has been placed. The nodules are usually 

 found near the top of the root system especially on deep- 

 rooted plants like alfalfa, often a large mass of them are 

 found around the top of the tap root. The arrangement 

 is characteristic with some plants like the lupine on 

 which the tubercles grow as bunches on the main root. 



Conditions for formation. It has been found that 

 certain conditions are favorable for the production of 

 the nodules. The soil must be well aerated and not acid 

 in reaction. In very rich soils the plant makes use of 

 the same source of nitrogen as do the grains and grasses, 

 the nitrates of the soil, and there is a tendency for the 

 nodules not to develop in such numbers as on a poorer 

 soil where the plant can not obtain sufficient nitrogen 

 from the soil, but in order to make a good growth must 

 get some nitrogen from the air. 



Soil inoculation. As was previously stated unless 

 the plant has tubercles on the roots no nitrogen can be 

 fixed and the plant will leave the soil poorer in nitrogen. 

 If the legume is to be a benefit to the soil, the tubercles 

 must be present. "While certain of the bacteria are pres- 

 ent in every soil, the kind 1 that will form nodules on 

 a new kind of legume may or may not be in the soil. If 

 they are not there, the soil must be inoculated. This can 

 be done most successfully by transferring a little soil 

 from a field on which the particular legume has grown 

 and on the roots of which there were an abundance of 

 nodules. This soil may be broadcasted over the field to 

 be inoculated or the sifted soil may be applied with a 

 drill. Especial precautions should be taken to see that the 

 higher parts of the field are inoculated for these can not 



