epidermal Tissue System

The epidermal tissue system forms the outer-most covering of the wholeplant body and comprises epidermal cells, stomata and the epidermalappendages – the trichomes and hairs. The epidermis is the outermostlayer of the primary plant body. It is made up of elongated, compactly
arranged cells, which form a continuous layer. Epidermis is usually single-layered. Epidermal cells are parenchymatous with a small amount ofcytoplasm lining the cell wall and a large vacuole. The outside of theepidermis is often covered with a waxy thick layer called the cuticle whichprevents the loss of water. Cuticle is absent in roots. Stomata are structurespresent in the epidermis of leaves. Stomata regulate the process oftranspiration and gaseous exchange. Each stoma is composed of two bean-shaped cells known as guard cells which enclose stomatal pore. Ingrasses, the guard cells are dumb-bell shaped. The outer walls of guardcells (away from the stomatal pore) are thin and the inner walls (towardsthe stomatal pore) are highly thickened. The guard cells possess chloroplastsand regulate the opening and closing of stomata. Sometimes, a few epidermalcells, in the vicinity of the guard cells become specialised in their shape andsize and are known as subsidiary cells. The stomatal aperture, guardcells and the surrounding subsidiary cells are together called stomatalapparatus The cells of epidermis bear a number of hairs. The root hairs areunicellular elongations of the epidermal cells and help absorb water andminerals from the soil. On the stem the epidermal hairs are calledtrichomes. The trichomes in the shoot system are usually multicellular.They may be branched or unbranched and soft or stiff. They may evenbe secretory. The trichomes help in preventing water loss due totranspiration