9. Investigations, reported in this bulletin, furnish conclusive proof that infected sweet clover soil can be used for inoculating alfalfa fields and with the same results as are obtained when the infected soil is obtained from an old alfalfa field. (Sweet clover is a tall, rank-growing, sweet-scented leguminous plant widely distributed over Illinois, especially along the roadsides in the northern and central parts of the state, and in many places in bottom lands in southern Illinois.) Page 324 10. This bulletin will be sent free of charge to any one interested in Illinois agriculture upon request to E. Davenport, Director Agricultural Experiment Station, Urbana, Illinois; and, if so requested, the name of the applicant will be placed upon the permanent mailing list of the Experiment Station, so that all bulletins will be sent to him as they are issued. Conclusions Page 327 NITROGEN BACTERIA AND LEGUMES (WITH SPECIAL REFERENCE TO RED CLOVER, COWPEAS, SOY BEANS, ALFALFA, AND SWEET CLOVER, ON ILLINOIS SOILS). BY CYRIL G. HOPKINS, CHIEF IN AGRONOMY AND CHEMISTRY. Among the several different classes or groups of bacteria there are two which are of special importance to agriculture because of their relation to the element nitrogen, this being commonly considered the most valuable element of plant food.[1] These two classes of bacteria are, first, the nitrifying bacteria, and, second, the nitrogen-gathering bacteria. THE NITRIFYING BACTERIA. The nitrifying bacteria are those which have the power to form nitrates. In the following brief discussion of this subject we include at least three species of bacteria which by their combined or successive action have the power to transform organic nitrogen into nitrate nitrogen, which is a suitable form of nitrogen for plant food. For the exact information which we now have regarding the nitrifying bacteria we are indebted to the researches of Pasteur and Schlösing and Müntz of France, Winogradsky of Russia, Warington of England, and others.