The Pulaskian., 1917-04-20

| fPrepared by the United States Depart ment of Agricultural
 From the earliest days of agricul- ture farmers have observed that the clovers, alfalfa, beans and peas en- riched the soil so that wheat, corn, cotton and similar crops gave better yields following them than when plant ed after the grains or grasses. The reason for this benefit to the soil, how ever is of recent discovery and the | broader practical application of the knowledge is just beginning to be eff fective.
 | Leguminous plants are readily dis tinguished, in most instances, by the characteristic form of their flowers, of which the garden pea is typical, and by the seed-bearing pods which split upon ripening, at both edges or su- lures. The most important difference, however, between leguminous and non- leguminous crop plants as they affect | the fertility of soil is the formation of nodules or tubercles, normally at tached to the roots of thriving plants of the legume family. These nodules vary greatly in size and shape. On the roots of red clover they are about the size of a pinhead and ovoid in | form; on alfalfa they are somewhat | larger and irregular in shape, ire quently forming in egg-shaped masses, the aggregate of which may be the size of very small marble, while on soy l 61ln a6c of the common pea both in size and | shape. For many years and until com 1 paratively recent times these nodules were thought to be form of root-gall | disease. In 1886 the scientists He'll riegel and Wilfarth discovered their real function in relation to the plants and to the soil.
 Function of Root NoduIes and NoduIe Bacteria.
 If a nodule on a living plant be cut open and some of the juicy substance in 1t be spread thinly upon a glass slide, examination under high power microscope will reveal an im- mense number of living single-celled organisms of the kind called bacteria. These nodule-forming bacteria, when In the soil pass into the minute root hairs of leguminous plants during their early growth and establish them selves In the outer layer of cells of the true roots, where they multiply rapidly and form the enlargements called .7odules.
 1 The nodule bacteria and the host plant are mutually helpful. The plant furnishes a home for the bacteria and | the bacteria in turn manufacture food for the plant.
 Plants like animals, require food materials for growth. Among the most important plant foods are com pounds of the element nitrogen, which as an invisible gas comprises about four-f1fths of the atmosphere. Nitro gen cannot be taken in directly by the leaves of plants as is carbon dioxid, but must first be combined with other clements to form soluble compounds of nitrogen which can be readily ab- sorbed by the roots. The nodule bac- teria of leguminous plants use nitro gen directly from the air as 1t circu- lates in the soil and convert 1t. into nitrogenous compounds which are uti- lized in the growth of the plants. Nonleguminous Crops.
 Nonleguminous crops, including corn and other grains, cotton, and the grasses, secure all of the nitrogen for their growth from the soil. All legu- minous crops, under normal conditions, obtain large part of their nitrogen through bacterial action directly from the air, and in general they contain a larger percentage of nitrogen and con.