500 FIXATION OR ASSIMILATION OF NITROGEN 



soil inoculation very frequently has given good results, 

 but it is a laborious and expensive process. To avoid 

 these disadvantages, Nobbe, in Germany, conceived the 

 idea of inoculating the soil or the seed before sowing 

 with pure cultures of organisms from the several legu- 

 minous crops usually cultivated on the farm. The pure 

 cultures were grown upon agar and gelatine media 

 impregnated with decoctions of the leaves of the various 

 legumes, and sold under the name of Nitragin. The 

 usual method of using the latter was to transfer the 

 culture to water or milk, and wet the seeds with the 

 liquid. When dry the seeds were sown, the right 

 organisms being necessarily supplied to the soil at the 

 same time. Hundreds of trials were made with 

 " Nitragin " in most European countries, and although 

 in a small percentage of cases the inoculated seed pro- 

 duced larger yields of crop than untreated samples, the 

 majority of the trials proved futile : the soil contained 

 plenty of the nodule organisms for infection of the young 

 leguminous seedlings, and to add more was superfluous. 



In 1904, Dr G. T. Moore, in America, came to 

 the conclusion that the failures of Nobbe's " Nitragin " 

 were largely due to the loss of vitality or virulence 

 of the nodule organisms contained in it, a result 

 brought about by cultivating them upon media rich in 

 nitrogen. There is little doubt that the nitrogen-fixing 

 power and power of infecting the roots of legumes is 

 greatly reduced by the presence in the soil of nitrates 

 and other nitrogenous compounds, and it is likely that 

 the virulence of the organisms is also checked by cultiva- 

 tion on artificial media containing considerable amounts 

 of combined nitrogen. Moore grew the organisms in 

 liquid media containing very small amounts of nitro- 



