A root hair is an elongation of the epidermal cells. It extends at right angles to the epidermis. The root air is 1 to 10 mm in length and 10microns in diametre. The No. of root hairs per unit area indicates the absorptive ca­pacity of the root. The cell wall of the root hair has 2 layers: The outer layer is pectic, while the inner layer is made of cellulose. The root hair does not have a separate nucleus. The nucleus of the epidermal cell also controls the activity of the root hair. The cell wall of the root hair is permeable to water.