List the characteristics of cork.

(a) Characteristics:

1. Outer Tissue: Cork is outer protective tissue of older stems and roots.

2. Dead cells: The mature cork cells become dead and filled with tannins, resins and air.

3. Compact Tissue: Intercellular spaces are absent. Cork is a compact tissue.

4. Suberin: Cork cells are impermeable due to deposition of suberin in their walls.

5. Multilayered: Cork consists of several layers of cells.

6. Shape: Cork cells are rectangular in outline.

7. Lenticels: At places cork bears aerating pores called lenticels.

(b) Formation:

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 while cells cut out on the inner side give rise to secondary cortex or phelloderm. The whole tissue (cork, cork cambium and secondary cortex) is called periderm.

(c) Functions:

1. Protection: Epidermis is the outer protective layer of the plant that prevents entry of pathogens and pests,

2. Water Loss: By presence of cuticle, it checks the rate of water loss from aerial parts,

3. Hair: Occurrence of epidermal hair produces an insulating stationary layer of air. (iv) Stomata. They regulate exchange of gases. Stomata are also the seat of major loss of water in transpiration.

Transpiration keeps the aerial parts cool.

4. Epiblema or epidermis of the root alongwith its root hairs takes part in absorption of water and minerals.