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

Explanation

1. In temperate and cold regions, the activity of cambium is influenced by seasonal variations.
2. In favourable conditions growth will be active. So plants require" large amounts of water and minerals. During unfavourable conditions plants are less active.

3. In spring, wood formed shows more number of xylem vessels having wide lumens. This is called spring wood or early wood.
4. During autumn, wood formed shows less number of xylem vessels with narrow lumens. This is called autumn wood or late wood.
5. Spring wood and autumn wood appear alternately in the form of circles in the T.S. of a tree trunk. These are called Growth rings or annual rings.
6. By counting the number of annual rings the age of tree can be estimated approximately.