How tree rings formed?

Answer 1

EASY EXPLANATION Trees form rings (also known as annual growth rings) because in temperate regions the vascular cambium, a type of lateral meristem that causes growth of secondary xylem, becomes dormant during the winter and later resumes growth in the spring. Because the cells are much smaller right before dormancy compared to the large cells right after dormancy, there is a clear difference, or ring, that is visible. This process occurs periodically every winter (every year), resulting in annual growth rings.

SLIGHTLY LESS EASY EXPLANATION

Vascular tissues of plants are of two types

1. Xylem

2. Phloem

And these 2 tissues are again of 2 types

1. Primary

2. Secondary

The primary vascular tissues are present in all vascular plants and are formed from a primary meristem called PROCAMBIUM . The secondary vascular tissues are found only in dicot plants because they develop from a special kind of meristem ( lateral ) called VASCULAR CAMBIUM which is seen only in dicots. The production of secondary vascular tissues is called SECONDARY GROWTH.

The vascular cambium produces secondary xylem to its inner side and secondary phloem to its outer side.

During spring, there is more activity in the plant due to the formation of new leaves, etc, hence the increased need for more water supply and thus more secondary xylem with large lumen is produced. This wood appears light in colour and is called EARLY WOOD or SPRING WOOD.

During autumn all the leaves fall off and there is not much need of xylem and hence the activity of vascular cambium decreases and less xylem with narrow lumen are produced. This wood appears dark and is called LATE WOOD or AUTUMN WOOD.

Thus every year two types of wood are formed which appear as a ring called ANNUAL RING or GROWTH RING.