Page:Popular Science Monthly Volume 63.djvu/342

338 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 binding free nitrogen, forming nitrogenous compounds which enrich the soil, thus increasing the yield of any crop benefited by such compounds. Whether alinit binds free nitrogen more actively in the presence 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 modifying 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 experimenting 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 consumed in making cultures or attempting to make cultures of the rhizobia of different species of leguminous plants. No field experiments were attempted, but some laboratory observations were made by inoculating 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 bacteriological laboratory of the Northwestern University School of Pharmacy at Chicago. Pure cultures of the rhizobia of white clover