Epidermal out growth:
Epidermal cells have unequally thickened walls, the outer and radial walls being much thicker than the inner walls. In some cases they may be so immense that the central lumen is almost obliterated. The walls are strongly cutinized, what is very important for protection against mechanical injuries and prevention of loss of water.
Different types of outgrowth are found in plant body.
(a) Hair: Few cells of the epidermis grow to form hair. Root hair is always unicellular while stem hair is usually multi-cellular.
- Stem hair helps in giving self defence of the plant
- Leaf hair reduces the rate of transpiration
- Root hair performs the function of absorption
(b) Trichome: Secretes sticky substance.
(c) Scaly leaf: It reduces the rate of transpiration.
(d) Spine: They are defensive in function.
(e) Papilla: It contains water.