Write a note on Epidermal Tissue system.

$\rightarrow$ On the basis of their structure and location, there are three types of tissue systems : Epidermal tissue system, the ground or fundamental tissue system and the vascular or conducting tissue system.

$\rightarrow$  Epidermal Tissue System :The epidermal tissue system forms the outermost covering of the whole plant body and comprises epidermal cells, stomata and the epidermal appendages - the trichomes and hairs.

$\rightarrow$ The epidermis is the outermost layer of the primary plant body. It is made up of elongated, compactly arranged cells which form a continuous layer.

$\rightarrow$ Epidermis is usually single layered. Epidermal cells are parenchymatous with a small amount of cytoplasm lining the cell wall and a large vacuole.

$\rightarrow$ The outside of the epidermis is often covered with a waxy thick layer called the cuticle which prevents the loss of water.

$\rightarrow$ Cuticle is absent in roots.

$\rightarrow$ Stomata are structures present in the epidermis of leaves. Stomata regulate the process of transpiration and gaseous exchange.

$\rightarrow$ In dicot plants, each stoma is composed of two bean-shaped cells known as guard cells.

$\rightarrow$ In grasses, the guard cells are dumb-bell shaped. The outer walls of guard cells (away from the stomatal pore) are thin and the inner walls (towards the stomatal pore) are highly thickened.

$\rightarrow$ The guard cells possess chloroplasts and regulate the opening and closing of stomata.

$\rightarrow$ Sometimes, a few epidermal cells, in the vicinity of the guard cells become specialised in their shape and size and are known as subsidiary cells.

$\rightarrow$ The stomatal aperture, guard cells and the surrounding subsidiary cells are together called stomatal apparatus.

$\rightarrow$ The cells of epidermis bear a number of hairs. The root hairs are unicellular elongations of the epidermal cells and help absorb water and minerals from the soil.

$\rightarrow$ On the basis of their structure and location, there are three types of tissue systems : Epidermal tissue system, the ground or fundamental tissue system and the vascular or conducting tissue system.