Name: These plants belong to a large family of a distinct type, called Leguminosce. Peas, Vetches, Beans, Red Clover, Alsike and Alfalfa belong to this great family - that is, the plants which farmers commonly term legumes and clovers. As generally used, the name 'clovers" includes Red Clover, Alsike, Dutch Clover, Crimson Clover, Alfalfa, Trefoil, Sweet Clover and other leguminous plants. Botanically, however, only the first four are clovers in the true sense; that is, they belong to the genus Trifolium, whereas Alfalfa, Trefoil and Sweet Clover belong to other genera.
Seed: When splitting a bean or a pea, the two halves seem to be kept together by the seedcoat only. One of them has a smooth, more or less shiny surface, on which no special texture can be discovered by the naked eye. Near the upper end of the other half is a peculiar organ consisting of two distinct portions. The upper is a bud (Fig. 5, B.), which corresponds to the similar formation in the grass embryo (see page 8). The lower, which lies close to the seed-coat, has a thicker upper part (Fig. 5, St.) and a tapering end (Fig. 5, Rad.), the former being the stem of the embryo, the latter its root or radicle. By far the greatest part of the seed (Fig. 5, Cot.) consists of the two cotyledons of the embryo. A leguminous embryo has thus two cotyledons whereas a grass embryo has only one. But a leguminous plant has no endosperm. The function of the endosperm of a grass seed, as stated on page 8, is to supply the embryo with food during germination. This function in a leguminous plant is performed by the two cotyledons, which are thick and filled with food.
Fig. 5. Section through a Bean. Four times natural size. B. - Bud. Rad. - Radicle.
St. - Stem. Cot. - Cotyledon.
Germination: When the seed of a leguminous plant germinates, the bud (Fig. 5, B.) develops into stem and leaves and the radicle (Fig. 5, Rad.) into the root of the plant. The stem of the embryo
(Fig. 5, St.) acts differently in different plants. In beans it grows in length and lifts the cotyledons (Fig. 5, Cot.), which gradually become flat and thin, above the ground. In peas it is short, and the cotyledons remain hidden in the soil for a long time, enclosed within the seed coat.
Root system: Leguminous plants are annual, biennial or perennial. When annual, like Crimson Clover, or biennial, like Sweet Clover, the primary root of the embryo always develops into a taproot. When they are perennial, a taproot may be found, or the underground system may consist of a rootstock, from which secondary roots are developed. With a rootstock the system is generally shallow and the plants depend on the surface soil for their food. A taproot usually penetrates to a considerable depth and the plant gets much of its food from the subsoil. Both secondary roots and taproots are characterized by small tubercles or clusters of nodules. The significance of these is discussed on page 18.
Stems: The stems of leguminous plants are erect or ascending as a rule. Only in a few cases, as in White Clover, are they creeping and able to develop secondary roots from their joints. Plants of this type form more or less spreading mats, in which individuals are difficult to recognize. The same is often the case when the stems, as in Flat Pea, develop from a spreading and extensively branched rootstock. In some species and genera, as in Flat Pea and Vetches, the stems are weak and are kept from falling to the ground by special organs on the leaves, called tendrils (see below).
Leaves: The leaves of leguminous plants are compound; that is, each leaf consists of a number of leaflets each completely separated from the others. The type - a leaf consisting of a number of pairs of leaflets and ending with an odd one - is that of Sainfoin (Plate 23). All other kinds are mere modifications of this type. Thus, when the leaflets are only three, as in Red Clover, Alfalfa, Sweet Clover and others, the well-known trifoliate leaf is obtained. In other species, such as the vetches (Plates 24 and 25) and Flat Pea, the blades of the upper leaflets are not developed; only their ribs remain and they are transformed into tendrils, the function of which is to support the weak stems.
Everybody knows that the plants in a field of peas or vetches are sometimes so firmly tied together, when the stand is dense, that to pull those at the end of a long row will move the plants at the other end. This is because the tendrils wind about the stems and branches of neighbouring plants and bind them together. These tendrils are marvellous things. Rub one gently with a bit of straw and it will answer to the touch by bending. Give it an opportunity to grasp the branch of an adjoining plant and it will embrace the branch so firmly that it will be impossible to loosen the plants without breaking the tendril. It has the faculty of feeling and the ability to act. Its sensitiveness is so great that some tendrils can feel a weight of only a quarter of a milligram.
Two appendages, the stipules, are attached to the base of the leaf stalk (Fig. 6, St.). They are generally narrow and insignificant, but sometimes, as in peas, they are shaped like the leaflets and are almost as large.
Fig. 6. Leaf of Alsikc Clover. Natural size. St. - Stipule.
Inflorescence: The flowers of leguminous plants are in clusters which, however different in appearance, are always constructed after the same principle. Sometimes they are long and comparatively sparsely covered with flowers, as in vetches (Plates 24 and 25). They are then called racemes. In other plants the racemes are short and the flowers crowded, as in Red Clover and Alsike. The inflorescences are then called heads. It is, however, impossible to draw a sharp line between a head and a raceme, the inflorescences, for instance, of Alfalfa (Plate 21) and Crimson Clover (Plate 17) being as much like short racemes as elongated heads.