Rhizodermis

Rhizodermis is the root epidermis (also referred to as epiblem), the outermost primary cell layer of the root.

Specialized rhisodermal cells, trichoblasts, form long tubular structures (from 5 to 17 micrometers in diameter and from 80 micrometers to 1.5 millimeters in length) almost perpendicular to the main cell axis - root hairs that absorb water and nutrients. Root hairs of the rhizodermis are always in close contact with soil particles and because of their high surface to volume ratio form an absorbing surface which is much larger than the transpiring surfaces of the plant.

With some species of the Fabaceae family the rhisodermis participates in the recognition and uptake of nitrogen-fixing Rhizobia bacteria - the first stage of nodulation leading to formation of root nodules.