Question

A T.S. of a trunk of a tree shows concentric rings which are known as growth rings. How are these rings formed?

Answer 1

Hint: The formation of rings is dependent on temperatures and seasons. These environmental factors stimulate certain compounds and this inconstant secretion causes rings on the tree trunk.

Step by step answer:
In a cross-section of the stem, the Growth ring is the increment of wood added during a growth period. In temperate regions, the growth period lasts for one year so the growth rings are called annual rings for temperate trees. In tropical regions, growth rings may not be annual. In addition, trees in temperate regions may sometimes have growth rings missing or rings may be deposited during a single year. This example of false rings is rings formed after insect defoliation.
The differences in growth rings produced in accordance to the production of conducting cells. For example, a distinction seen in growth rings, large growth rings are formed if cells are produced early and comparatively smaller growth rings are formed if cells are formed later or if growth is ended by a thick fibre layer or by parenchyma. During the spring season, the cambium is very active. It produces a very large number of xylary elements. Xylary elements are substances which produce xylem. These elements have vessels with wider cavities and are called spring or earlywood and also have a lighter color. During the winter season, the activity of cambium decreases and it produces xylary elements that have vessels with narrow cavities and are considered as autumn or latewood and are dark in color. Both rings appeared as alternate concentric rings and constitute an annual ring.

Note: Annual rings have also been used in dating ancient wooden structures. In temperate or cold climates the age of the tree can be determined by counting the total number of annual rings present at the base of the trunk or at the base of a large root.