modified epidermal cells of a root that absorb the majority of water and minerals.
root hairs (Wikipedia)
Drawing of root tip, showing young root hairs
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 visible to the naked eye and light microscope. They are found only in the region of maturation of the root. Just prior to, and during, root hair cell development, there is elevated phosphorylase activity.