question_answer 78)

  List the characteristics of cork. How are they formed? Mention their role.

Answer:

  As the plants grow older, the outer protective tissue (i.e., epidermis) undergoes certain changes. A strip of secondary moisten, called halogen or cork cambium replaces the epidermis of the stem. Cork cambium is a simple tissue, the cells are rectangular and their protoplast are vacuolated and contain tannins and chloroplasts. Cork cambium gives off new cells on its both sides, thus, forming cork (phellem) on the outer side and the secondary cortex or phelloderm on the inner side. The layer of cells which is cut by cork cambium on the outer side ultimately becomes several layered thick cork (bark) of trees. Cells of cork are dead and compactly arranged without intercellular spaces. The walls of cork cells are heavily thickened with an organic substance (a fatty substance), called suberin, which makes these cells impermeable to water and gases. Cork is protective in function. It's cells prevent desiccation (loss of water from plant body), infection and mechanical injury. It is light and does not catch fire easily. Due to these properties, cork is used as insulators, shock-absorbers, linoleum (used as flooring) and sports goods (in making of shuttle cocks, cricket balls, wooden paddles of table tennis, etc.). Commercial cork is obtained from the stem surface of cork oak tree (Quercus suber) found in Southern Europe and North Africa.