Fig. 2. Change in Ψ_w at various times after leaf discs were placed in the O₂ electrode. A, Intact disc. B, Peeled disc lacking the abaxial epidermis. For each point, two discs were obtained from the same leaf. One was used to measure photosynthetic O₂ evolution followed immediately by Ψ_w. The other disc was used to measure Ψ_w at time zero. The difference between the initial and final Ψ_w is shown on the ordinate. The figure shown alongside each curve is the average of all the values of initial Ψ_w measured for that treatment. This is a single representative experiment from two replicate experiments. O₂ evolution was 47–52 µmol m^–2 s^–1 (intact) and 42–49 µmol m^–2 s^–1 (peeled) in discs from plants with high Ψ_w, and 9–16 µmol m^–2 s^–1 (intact) and 34–43 µmol m^–2 s^–1 (peeled) in discs from plants with low Ψ_w. O₂ evolution was measured at an irradiance of 1200 µmol m^–2 s^–1 at 25 °C in saturated air containing 21 % O₂ and 1 % CO₂.