secondary growth
Increase in diameter of the roots and stems of certain plants (notably shrubs and trees) that results from the production of new cells by the cambium. It provides the plant with additional mechanical support and new conducting cells, the secondary xylem and phloem. Secondary growth is generally confined to gymnosperms and, among the angiosperms, to the dicotyledons. With just a few exceptions, the monocotyledons (grasses, lilies) exhibit only primary growth, resulting from cell division at the apical meristems.
