Explain The Formation Of Barks In Trees?

In plants some of the cortex cells are still able to divide. In most stems these cells lie immediately beneath the epidermis. When these cells divide they give rise to a layer of cork-cambium. The cork-cambium cells divide repeatedly. The new cells formed on the inner side of the cork-cambium become new cortex cells (secondary cortex) while those formed on the outer side become the cork cells. The cork cells are very closely packed without intercellular spaces. They become suberised, i.e. their walls become impregnated with a waterproof substance called suberin and they gradually lose their cell contents and die. The layer of cork formed beneath the split epidermis is a dead, waterproof and air-proof layer. All the cells outside the layer of cork eventually die because the cork cuts off all food supply to them. The layer of cork, together with the dead epidermis, forms the bark of the tree.

The formation of cork means that gaseous exchange can no longer occur through the stomata in the stem. However, at various place, usually below the original stomata, the cork-cambium, instead of producing closely packed cells, produces a mass of loosely fitting cells with numerous intercellular spaces among them. Such areas of loosely fitting cells in the bark are called lenticels.