33^ POPULAR SCIENCE MONTHLY. 



is used to inoculate soil either by spreading it broadcast or by sowing 

 or otherwise planting it with the seeds. It is not a nodule or root 

 tubercle-forming organism and does not enter into intimate symbiotic 

 or biologic relationship with plants. Its work is simply that of bind- 

 ing free nitrogen, forming nitrogenous compounds which enrich the 

 soil, thus increasing the yield of any crop benefited by such com- 

 pounds. Whether alinit binds free nitrogen more actively in the pres- 

 ence of gramineous plants must be more accurately determined by 

 experiment. 



In 1892, through a suggestion by Professor Conway MacMillan, 

 state botanist of Minnesota, the writer conceived the idea of modify- 

 ing leguminous tubercle bacteria by special culture methods so as to 

 induce them to develop in or upon the roots of gramineous plants, as 

 corn, wheat, oats, rye, and barley. Investigations in this direction 

 were begun at the Illinois Experiment Station at Champaign in 1893, 

 under the direction of Dr. T. J. Burrill. The time granted for experi- 

 menting was much too brief for obtaining any definite results. At 

 that time comparatively little was known of nodule bacteria (rhizobia) 

 in artificial culture media and most of the time allotted was con- 

 sumed in making cultures or attempting to make cultures of the rhizo- 

 bia of different species of leguminous plants. No field experiments 

 were attempted, but some laboratory observations were made by inocu- 

 lating sprouting corn grown in vessels filled with sterile sandy soil 

 with pure cultures of rhizobia grown upon corn extract agar media, 

 the supposition being that the corn extract would produce the desirable 

 changes in the organisms. After a few weeks the roots of the young 

 inoculated corn plants were examined microscopically to determine if 

 the presumably modified microbes showed any tendency to develop in 

 or on the root cells. In some instances numerous microbes were found 

 in the hair cells (trichomes) of terminal rootlets and in epidermal 

 cells and cells in apical areas, particularly at the points of secondary 

 root formation. While it was not experimentally proved that the 

 microbes present were rhizobia, it is highly probable that they were, 

 as the examination of control plants not inoculated, also grown in 

 sterile sandy soil, showed the absence of germs in root tissues and root 

 trichomes. It was apparent that the inoculated corn plants were 

 thriftier and of a deeper green than the control plants or those not 

 inoculated. Though the results are meager and far from conclusive, 

 yet the experiments pointed toward final, more positive results. The 

 experiment station research was now terminated, and other work kept 

 the writer from again taking up this line of research extensively until 

 early in 1902. At this time the investigations were begun in the bac- 

 teriological laboratory of the Northwestern University School of Phar- 

 macy at Chicago. Pure cultures of the rhizobia of white clover 



