A root hair is an elongation of the epidermal cell. It extends at right angles to the pilifeours layer. The root hair is 1 to 10 mm in length and 10 mm in diameter. The number of root hairs per unit area is a measure of the absorp­tive capacity of the root. The cell wall of root hair has two layers. ‘The outer layer is mainly composed of pectic substances, while the inner layer is made up of cellulose.

The wall composition varies in some instances as in Taxus baccata, where the outer wall is gelantinized and soil particles get inte­grated with it. In Com, the outer cell wall of root hair has no pectin, while Tradescantia, callose is present at the tip of the root hairs. Inside the cell is a large vacuole, which is continuous with that of the epidermal cell. There is no separate nucleus in the root hair. The nucleus of the epidermal cell con­trols the activity of the root hair also. The cell wall of root hair is permeable to water. The cytoplasmic layer functions as a differentially permeable mem­brane.