Fig. 1 Relationship between leaf measured with the pressure chamber (P) and that measured with the leaf-cutter psychrometer (L) when the sample was obtained with (A) the cutter of the psychrometer (L = 0.45P³ + 0.75P² + 0.67P - 0.34; r² = 0.68); (B) a new pair of razor blades (L = 1.02P + 0.11; r² = 0.84); (C) a disposable biopsy punch (L = 1.19P + 0.23; r² = 0.92); and (D) a biopsy punch, where the leaf was subsequently damaged with a nail punch (L = 0.23P³ - 0.50P² - 0.89P - 0.54; r² = 0.90). Values in (C) were the undamaged controls for (D); additional sets of data for undamaged discs obtained with the biopsy punch gave similar results to (C). Values are means ± 1 SE of 2 (C and D) or 3 (A and B) separate samples. The dotted line is the 1:1 line