(i) Cork is the outer protective tissue of older stems and roots.
(ii) The mature cork cells become dead and filled with tannins, resins and air.
(iii) Intercellular spaces are absent. Cork is a compact tissue.
(iv) Cork cells are impermeable due to deposition of suberin in their walls.
(v) Cork consists of several layers of cells.
(vi) Cork cells are reatangular in outline.
(vii) At places, the cork bears aerating pores called lenticles.
(B) Formation of cork: As plants grow old, cork is formed from a secondary lateral meristem called phellogen or cork cambium. It develops subepidermally in older stems and roots. Cells cut out on the outer side by cork cambium form cork or phellem white cell cut out on the inner side give rise to secondary cortex or phelloderm. The whole tissue (crok, cork cambium and secondary cortex) is called periderm.
(C) Functions of cork. See text.