I4 FODDER AND PASTURE PLANTS.
(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 tap-root. When they are perennial, a taproot may be found, or the under-ground 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