A root hair of a vascular plant, is a tubular outgrowth of a hair-forming cell on the epidermis of a plant root.
They are lateral extensions of a single cell, and invisible to the naked eye and light microscope. The function of root hairs is to collect water and mineral nutrients from the soil. This solution goes up through the roots to the rest of the plant.
Root hair cells survive for 2 to 3 weeks and then die off. New root hair cells are continually being formed at the tip of the root. This way, the root hair coverage stays the same.