Secondary growth can be defined as a phenomenon where, after the completion of primary tissue formation, more secondary tissues are developed to supplement dermal, vascular, and mechanical tissue systems in certain plants. Secondary growth is of two types, based on region: Stelar secondary growth and extra stelar secondary growth. In extrastelar region, cork cells, lenticels are produced towards the periphery by the activity of cork cambium.
Cork cambium cuts off cells outside and inner side. Cambium activity produces cork cells outside and secondary cortex inner side. These are thin-walled parenchymatous cells that develop from the inner side of the cork cambium. Cork cells are dead cells. The cork cambium (phellogen), cork (phellum), and secondary cortex (phelloderm) are collectively called periderm.
