What is the function of periderm?

A periderm can be define as a protective layer of the roots and stems. It consists of three parts named as phellogen (cork cambium), phellum (cork) and the phelloderm (secondary cortex).

It is the resistant layer against the mechanical injuries. It is efficient in preventing the loss of water from the plant. Due to the presence of inter-cellular spaces between the cells these cells allow the gaseous exchange with the outside atmosphere.