It has been proved experimentally that not only do the bacteria (rhizobia) of leguminous root tubercles have the power of assimilating or chemically binding the free nitrogen of the air, but also other soil bacteria and various simple algae and hyphal fungi. Undoubtedly the true ecological significance of these free nitrogen-assimilating functions of these organisms is to neutralize, balance or equalize the work of nitrifying and denitrifying (nitrogen-liberating) bacteria, which are very plentiful and widely distributed. More specifically considered, the organisms referred to chemically bind the free nitrogen of the air, forming nitrogenous compounds which may be taken up and assimilated by various plants. In the case of leguminous plants these nitrogen-assimilating bacteria (rhizobia) live within the roots (root tubercles) and supply the host directly with the enriching nitrogenous food compounds formed; in other instances the nitrogen-assimilating organisms live in the soil and the various higher plants as corn, wheat, etc., take up the compounds formed and deposited in the soil without being in actual biologic (symbiotic) association with them. These discoveries have suggested to the scientists interested in agriculture various possible improvements for increasing the yield of crops. Extensive and interesting experiments have already been made, and some noteworthy results have been obtained and, in other instances, investigations are under way which give promise of final useful results. Several processes for inoculating the soil or seeds with beneficial bacteria have been patented and, remarkable as it may seem, the slow, plodding German investigator is the first in the field with patent claims and 'practical' plans for utilizing bacteria in the interests of the farmer or the tiller of the soil.
The history of the discovery of the free-nitrogen-assimilating bacteria found in the root tubercles of leguminous plants is familiar to all botanists, but the general reader of science requires some detailed explanations and some specific statements regarding the subject in order that he may have reasonably clear ideas concerning the practical possibilities and probabilities of bacteria in modern agriculture. These necessary explanations will be given as we proceed.
The first to suggest a plan for practically utilizing root bacteria (rhizobia) and to secure letters patent for the process in Germany and in the United States were Nobbe and Hiltner, of Tharand, Germany. Since the wording of the specifications for a patent are required to be simple and intelligible to persons of ordinary technical learning, the scheme can best be presented by simply quoting the specifications. The following is the specification which forms part of letters patent No. 570,873 granted Nobbe and Hiltner in the United States, November 3, 1890:
