The common bottle cork is a product of

The cork cambium or phellogen cells divide periclinally cutting off cells towards the outside and inside. The cells cut off towards the out side become suberized and dead. These are compactly packed in radial rows without intercellular spaces and form cork or phellem. Cork is impervious to water due to suberin and provides protection to underlying tissues. The cells cut off from cork cambium towards inside add to the cortex and are called secondary cortex cells or phelloderm cells.