What is the primary growth of a root?

The very tip of the root is the root cap, a thimblelike cone of cells that protects the delicate, actively dividing cells of the apical meristem. The root's apical meristem has two roles: It replaces the cells of the root cap that are scraped away by the soil, and it produces the cells for primary growth. Cells produced during primary growth form three concentric cylinders of developing tissue (Figure 20-13). The outermost cylinder develops into the dermal tissue of the root. The middle cylinder-the bulk of the root tip-develops into the root's cortex (ground tissue). The innermost cylinder becomes the vascular tissue.

-Exploring life, Biology Textbook