Fixation of Nitrogen. 20& 



become infected by surface drainage as can the lower 

 areas. 



The disadvantages connected with the use of soil as an 

 inoculating agent, such as the expense, and the introduc- 

 tion of plant diseases, has led to the introduction of pure 

 cultures of the different kinds of nodule-forming bacteria 

 for the inoculation of the soil or the seed. These cultures- 

 have been used for many years but have never been as 

 successful as it was hoped they would be. At times the 

 inoculated plants would show an abundance of nodules, 

 again none could be found. This uncertainty of the re- 

 sult makes the use of the pure cultures inadvisable where 

 soil can be procured. 



Pure cultures of the legume bacteria are sent out by 

 the U. S. Department of Agriculture ; also by a number 

 of the Experiment Stations. These cultures are prepared 

 and sold by a number of commercial laboratories. They 

 are prepared for use in various ways. In some cases 

 the inoculating material is simply added to water and 

 sprinkled on the seed; in others a culture is made by 

 preparing a solution of the necessary food substances 

 which are sent with the pure culture. The usual method 

 of using the cultures is to mix the same with water and to 

 sprinkle the seed with it. The moistened seed is dried in 

 the shade to protect the bacteria from the injurious ef- 

 fect of sunlight and planted as soon as possible. 



The inoculation of the soil should be made whenever a 

 new legume is to be grown, when a previous crop has 

 shown no nodules, or where the nodules were few and 

 seemed to have no effect on the plant. The inoculation 

 need not be made when the same plant has been previ- 

 ously grown on the field and has shown tubercles. With 

 many legumes the seed is likely to be infected with the 



