When a root tip encounters an obstacle that resists penetration, the root cap becomes less pointed and the surface cells may slough off (Souty, 1987). Mechanical impedance decreases the rate of root elongation because of both a decrease in the rate of cell division in the meristem, and a decrease in cell length (rather than volume). Eavis (1967) found a decrease of 40% in the cell division rate at a root penetration resistance ( MPa) sufficient to decrease the root elongation rate by 70%. Cell length is decreased and the volume of the inner cortical cells may.
