It has been found where alfalfa shows thrifty vigor, is making a good stand, and is at least two years old, that on the roots are little nodules or wart-like protuberances. On fields where the alfalfa is unthrifty or failing to make a good stand, examination will probably fail to discover any of these nodules. Scientists tell us that these nodules are the homes of bacteria, microscopic vegetable organisms obtaining their sustenance from the nitrogen of the air and the starch of the plant; that they collect much more nitrogen than they need, the over-supply being taken up by the alfalfa, which, after these nodules are formed and occupied, takes no more nitrogen from the soil, but annually stores about its roots more from the air, thus adding to the nitrogen supply in the soil instead of taking from it as do all other farm crops except the legumes. Each legume--clover, alfalfa, cowpeas, etc.--has a distinct species of bacteria, or at least bacteria with a distinct development, excepting, as has been found, that Sweet clover (_Melilotus alba_) and Bur clover (_Medicago denticulata_) develop the same species as does alfalfa. BUYING INFECTED SOIL Several methods of preparing land for alfalfa by introducing its peculiar bacteria have been suggested, and practiced to some extent. Many farmers and experimenters have used with success infected soil upon their lands; soil from established alfalfa fields, or that from along the roads or creeks where the Sweet clover or Bur clover has been growing. This soil is spread upon the field or sown with alfalfa just before the seeding. If the drill is to be used the inoculated soil is spread on and harrowed in. If the seed is to be broadcasted, the infected soil may be harrowed in with the seed. It is better, however, to harrow this infected soil in thoroughly before seeding. Experiment stations recommend an application of two hundred pounds of such soil to every acre, but good results have been secured from half that quantity. This will depend very much upon the nature of the soil, and the subsoil especially. Many fields seem to have these bacteria waiting for the coming of alfalfa. Land that has been well manured and contains abundant humus, and land that is light and friable will usually respond to the bacterial life attached to the alfalfa seed. Most farmers who have established fields will sell soil to their neighbors, which should be from the top six or eight inches, and include roots, stubble and earth. Both Sweet clover and Bur clover are found in almost every neighborhood in the northern states, while the latter is very general in the South.