Name the protective tissues of plants. Explain them in detail with suitable examples.
The protective tissues in plants include epidermis and cork (phellem).
Epidermis It is the outermost covering of cells in plants. It performs protective function (protecting plants from some adverse conditions). It is usually made up of single layer of cells. In dry habitats, epidermis is thicker to protect the plant from undue loss of water.
On aerial parts of plant, epidermal cells often secrete a waxy, water resistant layer on their outer surface. This waxy covering aids in protecting the plant against loss of water, mechanical injury and invasion by parasitic fungi. The cells of epidermal tissue are present in a Continuous layer without intercellular spaces. Small pores are present on the epidermis of leaf. These pores are called as stomata. They are enclosed by two kidney-shaped cells called guard cells. They help in gaseous exchange and transpiration.
Cork As plants grow older, a strip of secondary meristem called cork cambium replaces the epidermis of stem. It is a simple tissue with only one type of cell. Cork cambium gives off new cells on both sides, forming cork. These cells are dead with no intercellular spaces and heavily thickened with suberin. Cork cells prevent dessication, infection and mechanical injury.