The periderm comprises 3 different layers – phellem, phelloderm and phellogen. Phelloderm is the inner side of cork cambium which is also known as the secondary cortex. In the secondary cortex of the cork cambium, cells of parenchymatous nature are found. These are living cells.
The meristematic tissue layer formed by the dedifferentiation of these parenchymatous cells is called phellogen or cork cambium. The outerside of the cork cambium is called the phellem or cork.