In rice plants, the diameter of root, thickness of cortex, number of cortical cell layers and width of cortical cells were measured in both mature and apical parts of crown roots. In mature part of roots, it could be proved that the thickness of cortex was in harmony with the diameter of root, but in the case of stele diameter, only slight change was noticed. The thickness of cortex was more dependent on the width of cortical cells than the number of cortical cell layers, because the former was proportional to the cortex thickness, but the latter was only decreasing with the distance from the base of root (Figs. 2, 3, 4). In the apical part of roots, at 200 μm level, the width of cortical cells was proved to be constant (3.8 μm) irrespective of root diameter or cortical cell layer number. Moreover, the width of cortical cells increased basipetally and it ranged from 13 to 31 μm in mature part (Table 1). In 1 mm diameter roots, the width of cortical cells increased basipetally up to 8 mm from the apical tip, at which the epidermal cell length reached its maximum (Fig. 9).