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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.). .

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 (Fig. 2124). 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 (Fig. 2125). These flowers are often dependent on insects for pollination.

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 (Fig. 2126). 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 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.

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.