Ncert Exercises & Solutions

39. A transverse section of the trunk of a tree shows concentric rings which are known as growth rings. How are these rings formed? What is the significance of these rings?

Concentric Rings The concentric growth rings are called annual rings. These rings are formed
activity due to the secondary growth. Secondary growth occurs in dicot trees due to the activity of cambium which is a meristematic tissue.

The rate of activity of cambium is more in spring so wood formed has larger wider xylem Cells, whereas wood formed in winter has narrower and smaller xylem elements. This results in the formation of two rings called growth rings.

By counting these rings, age of the tree can be determined. This branch of science is known as dendrochronology or growth ring analysis.

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