Periderm is a term used to refer as the multilayered system of tissues, which is usually made of cork or phellem. When plant's girth is increased due to its secondary growth, they replace epidermal tissues with periderm. Periderm constitutes phellem or cork cells whose walls are thick with a waxy substance called the suberin which protects the surface of the cells and waterproofs them. This secondary covering are formed on small woody plants from the phellogen, a meristematic cell layer which is responsible for the periderm's development.