Legumes

Read about Legumes in the Standard Cyclopedia of Horticulture

Legumes. The popular name given to the important group of plants included in the general Order Leguminosae comprises the herbs, shrubs, vines, and trees of the mimosa family (Mimosaceae), the senna family (Caesalpiniaceae), the krameria family (Krameriaceae;), and the pea family (Fabaceae; also called Papilionacea: or Phaseolaceae). In all, more than 7,000 species of plants are represented here, chiefly herbaceous in character; the arboreal forms occur in the temperate zones and are very frequent in the tropics. Many species are of unusual agricultural importance, both for forage, as cover-crops and green manure, and also for furnishing food for man. Among these may be noted alfalfa (Medicago sativa ), beans (Phaseolus sp.), clover, (Trifolium sp.), vetch (Vicia sp.), and peas (Pisum sp.). . Most of the native species of legumes, and all those cultivated as farm crops, belong to the Fabaceae or pea family. In these species the flower is of the pea type . The upper larger petal, called the banner, s, is exterior and folded over the others in the bud. The two lateral ones, situated below the banner, are the wings, w, w, while the lower pair, which are sometimes united, form the keel, k. The keel incloses the stamens and pistil, the latter being often bent at right angles to the ovary, or coiled. The stamens are either free or they form a tubular sheath surrounding the ovary. Often the upper one alone is free, leaving a slit along the upper side of the sheath. These flowers are often dependent on insects for pollination. The fruit of the legumes is a pod or legume, as in the bean . As a rule, the pods are one-loculed, and have the seeds arranged in rows. In some tribes they become several-celled by partitions which arise between the seeds. These pods become constricted at the partitions, and at maturity separate into short joints. The valves of the pods are generally papery or leathery, and open at maturity, often by a sudden snapping of the valves, which scatters the seeds. In other tribes, however, the pods are indehiscent, or do not split at maturity. The use of leguminous crops for soil improvement has long been recognized by good farmers as desirable. Aside from the general benefits of crop-rotation, the actual soil-enrichment is due largely to an accumulation of available nitrogen, and this gain in nitrogen is caused by the presence of minute soil-bacteria which possess the power of growing on the roots of the legumes, and then utilizing or "fixing" the free nitrogen of the air and converting it into food for succeeding crops. In view of these facts, it is evident that for the most successful growth of alfalfa, clover, vetch, and other legume crops, the proper organisms should be abundantly present in the soil. Certain localities are so supplied, as, for example, southern regions, which contain the cowpea organism naturally, and sections of the Middle West, which usually are inoculated with alfalfa organisms. Introducing new kinds of leguminous crops into a locality requires the introduction also of the proper bacteria for the legume selected, and this is best accomplished by either of the following methods of artificial inoculation: When a field is known to be well inoculated for a certain legume crop—for example, alfalfaas indicated by the presence of numerous nodules upon the roots of alfalfa plants growing therein, such soil is very desirable for the inoculation of other fields on the same farm or on nearby farms upon which alfalfa is to be sown for the first time. Two hundred pounds or more of sifted field-soil are sufficient for an acre. Transferring field-soil from any considerable distance is, however, expensive and subject to the danger of introducing troublesome weeds, insects, and plant diseases. Another method is that of seed- inoculation by means of pure cultures. For many years the United States Department of Agriculture has cultivated and distributed liquid pure cultures of the bacteria beneficial to legume crops, and commercial organizations have produced and sold various types of cultures with more or less successful results. The seeds to be treated are placed in a clean bucket, pail, or tub and a pure culture of these beneficial bacteria is applied a little at a time, thoroughly stirring the seeds in order to form a thin, moist coating of the culture on every seed. A comparison of the nitrogen-fixing nodules found upon the roots of different plants is interesting. The nodules are in reality roots or rootlets which, because of the presence of the nitrogen-fixing bacteria within their cells, have developed abnormally to form the characteristic swollen root tubereles or nitrogen-gathering nodules instead of the ordinary form of root. It is to be expected, as each kind of plant has a slightly different root-development, that the root-nodules will develop in a correspondingly typical manner. In fact, tne nitrogen-fixing root-nodule of any kind of plant is almost as definite and characteristic for that plant as the shape of the leaves or the arrangement of the leaves on the stem. CH The above text is from the Standard Cyclopedia of Horticulture. It may be out of date, but still contains valuable and interesting information which can be incorporated into the remainder of the article. Click on "Collapse" in the header to hide this text.

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References

• Standard Cyclopedia of Horticulture, by L. H. Bailey, MacMillan Co., 1963

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