(cork) The compact protective tissue that replaces the epidermis as the outer cellular layer in plants with secondary growth. It is the outer layer of the *periderm
and consists of numerous more or less isodiametric cells arranged in radial rows, with thick waxy suberized cell walls. Commercial cork is obtained from the cork oak Quercus suber, in which the same phellogen is active each year (see bark
). It consists of thin-walled unsuberized cork cells (phelloids) and is stripped from the tree approximately every nine years.