Periderm develops through the activity of cork cambium or phellogen.
Cork cambium or phellogen is the secondary meristem that develops generally from the collenchymatous cells of hypodermis, sometimes from the cells of the epidermis (apple), pericycle (Cimatis), phloem (vitis).
Phellogen gives rise to cork or phellem on the outer side and secondary cortex of phelloderm on the inner side.
Phellem or cork is the dead tissue with suberised cell walls. It is impermeable to water and is used commercially.
Quercus suber is commercial cork.
Secondary cortex or phelloderm is living tissue. It stores food and replaces the damaged primary cortex.
Phellem, phellogen and phelloderm are called periderm.
Periderm and fragments of epidermis form the protective tissues in an old dicot stem.
phellogen given rise to phellem which is used as commercial cork.