What is not a type of primary meristematic cell found in apical meristems?

The complete question is :

Which of the following is not a type of primary meristematic cell found in apical meristems?

a) Vascular cambium

b) Ground meristem

c) Procambium

d) Protoderm

Vascular cambium

Explanation:

Vascular cambium is a type of cell which is found in the lateral meristem and is involved in the secondary growth of the plants. It is the main growth tissue in the dicots.

The buttercups, oak trees and gymnosperms are some of the dicots in which the vascular cambium is the growth tissue.

This is not found in the monocots as they lack secondary growth. Auxin,  gibberellins and ethylene are some of the hormones involved in the secondary growth of the plant.