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growth ring (annual ring) Any of the rings that can be seen in a cross-section of a woody stem (e.g. a tree trunk). It represents the xylem formed in one year as a result of fluctuating activity of the vascular cambium. In temperate climates pale soft spring wood, characterized by large xylem vessels, is formed in spring and early summer. Growth slows down in late summer and a darker dense autumn wood with smaller xylem vessels is formed (see illustration). The age of a tree can be determined by counting the rings. Under certain circumstances two or more growth rings may form in one year, giving rise to false annual rings.
growth ring See TREE-RING.