FIXATION OF NITROGEN BY BACTERIA 189 



large scale on his estate at Lupitz in Germany. The 

 land there is of a light sandy character, and about half a 

 century ago was too poor to grow a profitable crop of 

 oats or rye without an expensive application of nitro- 

 genous and other fertilizers. However, after the growth 

 of lupins or serradella, manured with superphosphates 

 and kainit, the barren soil has improved so much that 

 large yields of cereals as well as leguminous crops 

 have been obtained annually from it for over fifty years 

 in succession, and the land has become three times as 

 rich in nitrogen as it was at first, although no nitro- 

 genous manure has been applied during this long period. 



Results such as these created a special interest in the 

 investigation of the sources from which leguminous plants 

 obtain their stock of nitrogen, and many distinguished 

 workers applied themselves to the subject during the 

 lasl^Kalf of the nineteenth century. 



2. When wheat, mustard, or other non-leguminous 

 plants are grown in plots containing field or garden 

 soil of known chemical composition, the total amount of 

 nitrogen in the fully developed plants and the soil at 

 the end of the experiment is equal to that contained 

 originally in the soil and the seeds which were sown. In 

 the case of beans, however, and vetches or other legu- 

 minous plants grown in the same soil under similar 

 conditions, it is found that the nitrogen present in the 

 soil and the plants when fully grown is very much 

 greater than that which was supplied at the beginning 

 of the experiment in the soil and seed. They are able 

 to accumulate large quantities of nitrogen in a manner 

 not possessed by cereals or other crops, and from a 

 source which is evidently not available to the latter. 

 Acquaintance with facts of this kind suggested the 



