Increase in the girth of plant (organ) takes place by
a)	Vascular cambium	b)	Cork cambium
c)	Both (a) and (b)	d)	Root and shoot apical meristem

(d)

Increase in the girth of plants (organ) takes place by vascular and cork cambium.

Root Apical Meristem (RAM), Shoot Apical Meristem (SAM) and intercalary meristem are responsible for the primary growth to the plants and they principally contributes to the elongation of the plants along their axis.

In the dicotyledons and gymnosperms, the lateral meristems, vascular cambium and cork cambium appear later in life. These are the meristems that causes increase in the girth of the organ in which they are active. This is known as the secondary growth of the plant