Rubber-Bearing Plants

plants that form and contain natural rubber in certain of their parts.

Depending on the tissues in which the rubber accumulates, rubber-bearing plants are divided into latex plants (the rubber contained in a milky sap, or latex), parenchymal (in the parenchyma of the axial organs, the stems and roots), and chlorenchy-mal (in the green tissues of young shoots and leaves). Latex trees are of commercial importance, since they both store rubber in comparatively large quantities and surrender it easily. The most important of these plants is the Para rubber tree (Hevea brasilien-sis), which provides 95 percent of the world’s natural rubber. The remaining 5 percent is obtained from other tropical latex trees of the genera Sapium and Manihot (family Euphorbiaceae), Ficus and Castilloa (family Moraceae), and Landolphia (family Apocynaceae). The herbaceous latex-bearing plants of the family Compositae—the tau saghyz (Scorzonera tau-saghyz), the kok-saghyz {Taraxacum kok-saghyz), and the krym-saghyz (7– gym-nanthum) —which grow in the temperate zone (including that of the USSR), contain small amounts of rubber in the roots. They are not cultivated, however, being commercially unimportant. The parenchymal rubber-bearing plants include the Mexican guayule (family Compositae). Chlorenchymal rubber-bearing plants (for example, a number of species of genera Senecio and Centaurea) are not used industrially.