Question

Which tissue is responsible for the increase in diameter of the stem?

Answer 1

Hint: It exists in the radial portion of the stem or root. It increases the thickness of the stem or root. It is a part of secondary growth. It doesn’t occur in all plants, like in herbaceous plants, it’s absent. It occurs mostly in dicots and seen very prominently and noticeably in woody plants but it doesn’t occur in monocots.

Complete explanation:
Lateral meristems help in the growth of the girth or diameter of the stem as well as roots. It thus helps in the process of secondary growth. The cork cambia and the vascular cambia collectively are responsible for the secondary growth of plants. They are parts of the lateral meristem.
The vascular cambium which is found in between the primary xylem and primary phloem (within the vascular bundle) divides and forms the secondary xylem (tracheids and vessel elements) interiorly and secondary phloem (sieve elements and companion cells) exteriorly. Its cells contain lignin which is the primary component of wood. It provides strength and makes the stem hard. The xylem and the pith from the wood of a woody stem in a plant.
Cork cambium produces cork cells and phelloderm. Cork cells contain waxy substances that can repel water. The cork cells along with the phloem form the bark. This provides mechanical strength and protects the plant against any kind of physical damage. It also helps to reduce water loss. Phelloderm, which is a permanent tissue, grows inward from the cambium and helps in the defense mechanism of the plant. It gives rise to the periderm along with the cork cambium and the cork cells of the plant.

So, the correct answer is lateral meristem which includes the cork and the vascular cambium.

Note:
The vascular cambium also gives rise to annual growth rings. When the cells of the secondary xylem have a large internal diameter and their primary cell walls are not thickened during the spring season, it is known as early wood or spring wood. When the secondary xylem develops thickened cell walls, late woo, or autumn wood is formed which is much denser than the early wood. This causes an alternation of early and late wood. There is a large seasonal decrease in the number of vessel elements and significantly a rise in the number of tracheids as a result of which annual rings are formed. These are in the cross section of the stem.