The correct answer is Periderm.
In plants which undergo secondary growth, the periderm, replaces the epidermis and becomes bark.
The periderm is a multilayered tissue that is different from the epidermis which is single layered. It is made of cork cells (phellem) , phelloderm and phellogen (or cork cambium).
Cork cells are nonliving cells found covering the outside of roots and stems to provide protection and insulation to the plant.
The periderm serves to protect the plant from injury, pathogens, excessive water loss and provides insulation for the plant.
