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.
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