cambium

cambium , thin layer of generative tissue lying between the bark and the wood of a stem, most active in woody plants. The cambium produces new layers of phloem on the outside and of xylem ( wood ) on the inside, thus increasing the diameter of the stem . In herbaceous plants the cambium is almost inactive; in monocotyledonous plants it is usually absent. In regions where there are alternating seasons, each year's growth laid down by the cambium is discernible because of the contrast between the large wood elements produced in the spring and the smaller ones produced in the summer. These are the annual rings, by which the age of a tree can be established. A tree dies when it is "ringed," or girdled, i.e., cut through the cambium layer. The cork cambium, which lies outside the phloem layer, produces the cork cells of bark .

cambium (lateral meristem) A plant tissue consisting of actively dividing cells (see meristem) that is responsible for increasing the girth of the plant, i.e. it causes secondary growth. The two most important cambia are the vascular (or fascicular) cambium and the cork cambium. The vascular cambium occurs in the stem and root; it divides to produce secondary xylem and secondary phloem (new food- and water-conducting tissues). In mature stems the vascular cambium is extended laterally to form a complete ring: the sections of this ring between the vascular bundles comprises the interfascicular cambium. Compare apical meristem.