Real Dictionary

cambium in American English
a layer of formative cells between the wood and bark in dicotyledonous plants: these cells cause the girth of the stem to increase by dividing and differentiating to form new xylem and phloem tissue, which will eventually become wood and bark
noun: a layer of delicate meristematic tissue between the inner bark or phloem and the wood or xylem, which produces new phloem on the outside and new xylem on the inside in stems, roots, etc., originating all secondary growth in plants and forming the annual r

cambium in British English
noun: a meristem that increases the girth of stems and roots by producing additional xylem and phloem