Question

Phellogen cuts off closely arranged parenchymatous cells on the outer side instead of cork cells. Why?

Answer 1

When the girth of the plant increases the layers need to be replaced by new protective layers. To fulfill this need, a meristematic tissue develops in the cortex region. This meristematic tissue is called cork cambium or phellogen. The phellogen cuts off cells on both sides. The outer cells differentiate into cork or phellem. The inner cells differentiate into secondary cortex or phelloderm. As the cork cambium is impervious to water due to suberin deposition in the cell wall. The cells of the secondary cortex are parenchymatous are pushed towards the periphery and after some time the cells die due to the pressure towards them.