Question

How does the cork act as a protective tissue?

Answer 1

Plants develop a cambium ring, called crock cambium (phellogen) in the outer region during secondary growth. Cork is formed by cork cambium towards the outer side and they help by providing protection.

Complete answer:
As the secondary growth continues for many years, the stem constantly grows in girth (thickness) due to the activity of lateral meristem. Due to increase in thickness outer tissue breaks. To avoid such breaking or external tissue, the plants develop a new cambium ring, called cork cambium (phellogen) in the outer region. Cork cambium produces dead cells or cork (phellem) outer side and living cells of secondary cortex (phallodeum) inner side. The layers of cork, cork cambium and secondary cortex form the protective covering called periderm.

The cork cells are highly lignified and check the loss of water from the surface of the stem.Most of the cells of cork (phellem) are dead. But at some places living cells are also found. In dead cells, suberin is present. Suberin is a waterproof waxy substance which prevents water loss. And also they are impermeable to water, thus protecting the tissues from desiccation and pathogenic infection. In cork, there are living cells at some places and suberin is not deposited in these places.

Additional information: All the tissues which occur outside the cork cambium are collectively termed as rhytidome. Rhytidome includes cork and tissues which become dead due to the pressure of cork.

Note: Cork acts as protective tissue because of suberin deposition in dead cells compactly arranged without intercellular spaces. It forms high quantity and secondary cortex is in less quantity because activity of cork cambium is more towards the outside. The highest activity of cork cambium is in the winter season.