=Green Manuring.=--The system of green manuring, as formerly understood and practiced, had two purposes in view. One was to supply the soil with needed humus; the other to furnish winter protection and prevent washing. The practice is a very old one and has much to commend it. Not only do plant roots draw up fertility from considerable depths, to be afterward deposited in the superficial soil when the growing crop is turned down by the plow, but the process favors chemical changes in the soil by the admission of air and sunlight and by the decomposition of leaves, stems and roots. But nothing whatever in the way of new fertility is added by turning down a rye crop, for instance. [Illustration: Crimson or Scarlet Clover, a Nitrogen Gatherer.] =Cultivating the Legumes.=--The present system of green manuring contemplates something in addition to what was formerly gained, for agricultural sciences now recognizes the fact that nitrogen, the most expensive element of fertility, can be taken from the air and added to the plant food in the soil by means of certain plants which have the peculiar habit of regularly forming little tubercles or lumps on their feeding roots. These lumps are to be found on plants in perfect health, and are not parasitical in any hostile sense. The lumps are filled with small living organisms called bacteria, and, hence, have been called bacteroid tubercles. The minute tenants slowly but surely secrete nitrogen, and put it in a form adapted to plant growth. The plants which bear these root lumps belong to a group called legumes, of which clover, peas, beans, vetches, etc., are familiar examples. Curiously enough, nearly all the leguminous plants are thus fitted by nature by means of the root lumps to act as soil enrichers, and these plants have, therefore, assumed the highest agricultural significance. It is well known that such crops as cowpeas, crimson or scarlet clover, common red and pea vine or sapling clover, Soja beans, vetches, etc., can be used to add nitrogen to the soil in commercial quantities. The gain of new material, expressed in money, has been estimated as high as $25 per acre. This, therefore, is the avenue through which the farmer can most economically supply nitrogen to his land. If he will exercise all the economy heretofore suggested in the care of natural manures, and will grow legumes, he will not have much occasion to buy nitrogen in the market. =Grass vs. Clover.=--An idea of the great fertilizing value of the leguminous plants as compared with grasses may be obtained by a study of the following analyses from U. S. Farmers' Bulletin No. 16, by Dr. E. W. Allen, on "Leguminous Plants for Green Manuring and for Feeding": Fertilizing Value in Crop. Assumed Per Acre. Yield. Per Acre. Nitrogen. Phos. Acid. Potash.