As plants grow older, the outer protective tissue of the stem changes into cork. How does this happen??

List two salient features of cork.

Cork is formed by a secondary lateral meristem called cork cambium or phellogen. As the plants grow, the cork cambium produces secondary cortex on the inner side and cork on the outer side. Further as the cells mature, the older cells become dead and filled with tannins, resins and air. Their walls become impermeable due to deposition of suberin. So, as it grows older, the outer layers change to form cork.

Features of cork are:

1) It is impermeable to water.

2) Acts as the insulating material and protects plant from mechanical injury, temperature changes, etc.