cork, protective, waterproof outer covering of the stems and roots of woody plants. Cork is a specialized secondary tissue produced by the cork cambium of the plant (see meristem, bark). The regularly arranged walls of cork cells are impregnated with a waxy material, called suberin, that is almost impermeable to water or gases. Commercial cork, obtained from the cork oak, is buoyant in water because of the presence of trapped air in the cavities of the waterproof dead cells. It is also resilient, light, chemically inert, and, because of the suction cup action of the cut cells, adhesive. These qualities make cork valuable for bottle stoppers, insulating materials, linoleum, and many household and industrial items.