In plants, a tube or an assemblage of tubes, through which the sap is transmitted along the leaves. The term is more properly applied to the finer and more complex ramifications, which interbranch with each other like net-work; the larger and more direct assemblages of vessels being called ribs and nerves. Veins are also found in the calyx and corol of flowers. The vessels which branch or variously divide over the surface of leaves are called veins.