318 SYMBIOTIC NITROGEN FIXATION 



For small plots, such soil can be directly harrowed into the soil to 

 be inoculated after being spread (about one bushel per acre) in moist 

 condition on a cloudy or rainy day." 



Commercial Cultures. Because inoculation by means of soil from 

 old fields may transmit fungus diseases, weed seed, and necessi- 

 tates the transference of large quantities of soil numerous workers 

 have endeavored to inoculate with pure cultures. The first 

 attempt was made by Nobbe and Hiltner who placed on the market 

 a preparation called "nitrogin." Eight kinds were prepared suit- 

 able for the different legumes and were sent out on- gelatin. Some 

 of the results were satisfactory, but on the whole the percentage of 

 failures was so great that the method was largely discredited. 



Later the subject was investigated by Moore who considered the 

 failures of Nobbe due to the fact that he had grown his cultures on 

 gelatin. This contained combined nitrogen in abundance and the 

 bacteria lost their virulence and no longer possessed the power of 

 forcing their way into the roots of leguminous plants and producing 

 nodules. Moore used a nitrogen-free medium for the growth of 

 his cultures, thus increasing their nitrogen-fixing power. They 

 were distributed on cotton. Later liquid cultures were used and 

 since that time many different media, including even soil humus 

 have been used by different workers with varying degrees of 

 success. As a result, at the present time some commercial cultures 

 are being put upon the market which are probably just as efficient 

 as are the natural-occurring soil organisms. However, some work- 

 ers claim to have developed organisms possessing a high physio- 

 logical efficiency. But after taking all the tacts into consideration, 

 one must conclude that at the present time the pure cultures have 

 little advantage over the natural-occurring organisms. 



REFERENCES. 



Lohnis: Handbuch der Landwirtschaftlichen Bakteriologie. 



Lafar: Handbuch der Technischen Mykologie. 



Voorhees and Lipman: A Review of Investigations in Soil Bacteriology, U. S. 

 Dept. Agr., Off. Exp. Sta. Bull. 194. 



Whiting: A Biochemic Study of Nitrogen in Certain Legumes, Illinois Exp. 

 Sta. Bull. 179. 



Burrill and Hansen: Is Symbiosis Possible between Legume Bacteria and Non- 

 legume Plants, Illinois Exp. Sta. Bull. 202. 



