annual rings
Concentric rings visible on the wood of a cut tree trunk or other woody stem. Each ring represents a period of growth when new xylem is laid down to replace tissue being converted into wood (secondary xylem).
The wood formed from xylem produced in the spring and early summer has larger and more numerous vessels than the wood formed from xylem produced in autumn when growth is slowing down. The result is a clear boundary between the pale spring wood and the denser, darker autumn wood. Annual rings may be used to estimate the age of the plant (see dendrochronology), although occasionally more than one growth ring is produced in a given year.
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