Which type of meristem is responsible for the increase in the girth or diameter of a plant?

Lateral meristem, also known as the cambium, is a type of meristem found in the stems and roots of woody plants. It runs parallel to the central axis of the organ and is responsible for the secondary growth or increases in the girth of the plant. The lateral meristem divides to produce new cells that differentiate into secondary xylem and phloem tissues, which form the annual rings in tree trunks. The activity of the lateral meristem allows the plant to increase its diameter and provide structural support as it grows taller.

Intercalary meristem is responsible for the elongation of the internodal regions and the development of branches at the nodal areas. Apical meristem is responsible for the primary growth or elongation of the plant and is found at the tips of roots and shoots primary meristem, is a general term that refers to the embryonic tissue that gives rise to the primary plant body during development.