Cork

Cork, or phellem, is a protective plant tissue produced by the cork cambium. Mature cork consists largely of dead biological cells whose cell walls contain suberin, a material that limits passage of water. Cork forms part of the outer protective covering of mature plant stems and the root; it is not a name for every component of bark.

Commercial cork comes from the especially thick outer bark of Quercus suber. Comparing actively forming cork with other plant tissues connects its useful barrier properties to gene expression involved in suberin production. Such comparisons have identified candidate pathways in cork differentiation rather than treating the material simply as inert packing.^[ref]