gum

noun

(L. gumen: gum) A viscid sap exuding from stems, often air hardened. Any of a variety of substances obtained from plants. Typically they are insoluble in organic solvents but form gelatinous or sticky solutions with water. Most gums are complex polysaccharides. Commercially important examples are gum arabic and gum tragacanth. Gum arabic (or gum acacia) is obtained from various acacia trees; it is used in the manufacture of confectionery, cosmetics, linctuses and other medicinal products, and gummed labels. Gum tragacanth, extracted from trees of the genus Astragalus, forms a thick mucilage in water; it is used in the manufacture of pills and confectionery and as a sauce thickener. Gum resins are mixtures of gums and natural resins. Gums are produced by the young xylem vessels of some plants (mainly trees) in response to wounding or pruning. The exudate hardens when it reaches the plant surface and thus provides a temporary protective seal while the cells below divide to form a permanent repair. Excessive gum formation is a symptom of some plant diseases.