A. Characteristics of cork:
(i) Cork is the outer most water proof protective tissue present in older or mature woody stems and roots.
(ii) Cork composed of many layers of dead cells.
(iii) The mature cork cells become dead and filled with tannins, resins and air.
(iv) Cork cells are compactly arranged without intercellular spaces.
(v) Cell have thick walls with the deposition of a water proof material, suberin.
(vi) Lenticles (pores) found on the outer surface of cork which help in aeration of inner tissues.
B. Formation of cork: Cork is formed by a secondary lateral meristem called cork cambium or phellogen. As plants grow older, some cells below the epidermis become meristematic and forms the cork cambium or phellogen. The activity of phellogen produces phellem or cork towards outside and phelloderm or secondary cortex towards inside. The phellem, phellogen and phelloderm together constitute the periderm. It acts as a secondary protective tissue for the stems.
The cells of phellem or cork are normally suberized and impervious to water and air.
C. Functions of cork: Cork performs protective functions in the following ways:
(i) Cork cells being highly suberised and thick-walled protect the inner tissues.
(ii) It protects the inner tissues from the attack of microorganisms and mechanical injury.
(iii) Suberin being water-proof, prevents loss of water.
(iv) Lenticles allow exchange of gases.
(v) Cork is ligh and does not catch fire easily.
(v) Provides insulation from extream hot and cold temperatures.
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