A root hair, or absorbent hair, the rhizoid of a vascular plant, is a tubular outgrowth of a trichoblast, a hair-forming cell on the epidermis of a plant root. As they are lateral extensions of a single cell and only rarely branched, they are invisible to the naked eye. They are found only in the region of maturation of the root. Just prior to the root hair cell development, there is a point of elevated phosphorylase activity.