A cylindrical layer of tissue in the stems and roots of many seed-bearing plants, consisting of cells that divide rapidly to form new layers of tissue. Cambium is a kind of meristem and is most active in woody plants, where it lies between the bark and wood of the stem. It is usually missing from monocotyledons, such as the grasses. &diamf3; The vascular cambium forms tissues that carry water and nutrients throughout the plant. On its outer surface, the vascular cambium forms new layers of phloem, and on its inner surface, new layers of xylem. The growth of these new tissues causes the diameter of the stem to increase. &diamf3; The cork cambium creates cells that eventually become bark on the outside and cells that add to the cortex on the inside. In woody plants, the cork cambium is part of the periderm.