The cuvette allows micromanipulation on the lower leaf surface by micropipettes inserted through small holes in the cuvette wall. Micropipettes were drawn from 1.5-mm borosilicate glass capillaries with a pipette puller (L/M-3P-A; List). Tips were ground to a diameter of approximately 5 μm. Mineral oil (M8662; Sigma-Aldrich) was applied to pores by approaching the oil-filled pipette to a pore and gently pressurizing it manually by pressing a rubber ball. In each experiment, six to 20 pores with a spacing of at least 2 mm were selected. Either the observed pore or the observed pore plus the adjacent pores was sealed with oil. In an additional experiment, which was only used for the model parameter estimation, only the adjacent pores were sealed (leaving the observed central pore free). In all experiments, a control sample of the same size as the treatment sample was observed to detect and correct for interday variability, which, however, was found to be small.