periderm

A protective tissue of secondary origin, comprising the phellogen, phellem, and phelloderm and replacing the epidermis as the outer cellular layer of the stem and root in plant axes exhibiting secondary growth. In such tissue the functions of stomata are performed by lenticels. Periderm also often develops at the site of a wound or other recently exposed surface, thus helping to prevent the entry of pathogens. Compare bark , rhytidome.