"The individual bacteria are very short-lived," he continued, "and products of decay soon begin to accumulate in the tubercles. These products contain, in combined form, nitrogen which the bacteria have taken from the air, and in this form it is taken from the tubercles and absorbed through the roots into the host plant and thus serves as a source of nitrogen for all of the agricultural legumes. "It should be kept in mind, of course, that the red clover has one kind of nitrogen-fixing bacteria, that the cowpea has a different kind, and that the soy bean bacteria are still different, while a fourth kind lives on the roots of alfalfa and sweet clover." "How much infected sweet clover soil would I need to inoculate an acre of land for alfalfa?" asked Mr. West. "If the soil is thoroughly infected, a hundred pounds to the acre will do very well if applied at the same time the alfalfa seed is sown and immediately harrowed in with the seed. If allowed to lie for several hours or days exposed to the sunshine after being spread over the land the bacteria will be destroyed, for like most bacteria, such as those which lurk in milk pails to sour the milk, they are killed by the sunshine." " That's right," said the grandmother. "That's the way to sterilize milk pails and pans and crocks. I like crocks better than pans. They don't have any sort of joints to dig out." "Of course," continued Percy, "a wagon load of infected soil will make a more perfect inoculation than a hundred pounds, and where it costs nothing but the hauling it is well to use a liberal amount." "How deep should it be taken?" asked Mr. West. "About the same depth as you would plow. The tubercles are mostly within six or eight inches of the surface. The bacteria depend upon the nitrogen of the air and this must enter the surface soil. Sometimes in wet weather the tubercles can be found almost at the surface of the ground, and when the ground cracks one can often find tubercles sticking out in the cracks an inch or two beneath the surface but protected from direct sunshine. "These bacteria have power to furnish very large amounts of nitrogen to such a crop as alfalfa. The Illinois Station reports having grown eight and one-half tons of alfalfa per acre in one season. It was harvested in four cuttings. The hay itself was worth at least $6 a ton above all expenses, which would bring $51 an acre net profit for one year. Of course this was above the average, which is only about four and one-half tons over a series of several years. But suppose you can save only three tons and get $6 a ton net for it, as you could easily do by feeding it to your cattle and sheep. That would bring $18 an acre or six per cent. interest on $300 land. I am altogether confident that this could be done on your sloping hillsides, with their rich supplies of phosphorus and other mineral foods, provided, of course, that you use plenty of ground limestone and thoroughly inoculate the soil."