Phaseolus vulgaris plants with expanding primary leaves were subjected to dark-light or light-dark transition at a root temperature of 25 o C, or to root cooling to 10 o C. Illumination or darkening caused rapid changes in water flux through the plants and in epidermal turgor pressure when analysed by pressure probe. However, these were not concurrent with variations in bulk leaf water potential and turgor pressure as determined by the pressure chamber method. In addition, the turgor pressure of epidermis measured with the pressure probe was invariably 0.05 to 0.15 MPa lower than that measured in bulk tissue with the pressure chamber. Cooling roots to 10 o C induced water stress and wilting