Epidermal cells

Observe the outermost layer of cells in plants

What do you notice?

This is the single layer of cells called epidermis .

They are flat with outer and side walls are thicker than the inner wall

It is present all through the plant and protects the plant parts .

Since it has to protect, these cells do not have intercellular spaces .

The epidermal cells on the aerial surface (part facing outward) secrete a waxy, water-resistant layer .

This aids :

• Protection against loss of water
• Mechanical injury 
• Invasion by parasitic fungi

The epidermis is thicker in dry areas to protect plants from water loss. They also have a layer of chemical substance called cutin which gives the plant waterproof quality .

Stomata

Observe this image;

Look at the small pores present between the epidermal cells .

These are called stomata .

• The pore called stomata is enclosed by two kidney-shaped cells called guard cells .
• Exchange of gases (respiration in plants) takes place through stomata.
• Transpiration (loss of water in the form of water vapour) also takes place through stomata

There are root hairs extending from the epidermal layer .

Why is this so?

The root epidermis is responsible for water absorption

To increase surface area of absorption , they bear long hair-like structures called root hair.

Branch

Have you observed the outer layer of a branch of a young plant and that of a tree?

Why are they different?

The outer protective tissue of plants undergo certain changes with time

A strip of secondary meristem replaces the epidermis of the stem. 

Cells on the outside are cut off from this layer to form several-layer thick cork (bark of the tree)

• Cork cells are dead
• Cells are compactly arranged
• They do not have intercellular spaces
• They have a chemical called suberin in their walls
• Suberin makes sure that gases and water cannot pass through
• Thus it protects the plants from mechanical injury and water loss by evaporation.