Fig. 5. Mean (b) total leaf water (_W(PSY)), and (b) osmotic () potentials determined using standard thermocouple psychometric techniques, and the (a) resultant pressure (_P) potential (i.e., _P = _W(PSY) – ) for fully expanded sunlit flag leaves of spring wheat at midday (MD) (solar noon) and at midafternoon (MA) (2.5 h after solar noon) on day after 50% emergence (DAE) and development stage given during the 1994 growing season. Letters e through j in legend of panel (b) denote DAE and number of days between measurement dates and last irrigated for (Dry:Wet) treatments during the third (e, f) and fourth (g, h, i, and j) soil dehydration cycles (Fig. 1c). Vertical dashed lines in panels (a) and (b) delineate the third and fourth soil dehydration cycles illustrated in Fig. 1c. Horizontal arrows in panel (a) denote overall trend in values of _P across treatments. Each mean datum for _W(PSY), , and the resultant _P was derived from three repeated measures across four treatments and three replications (3 x 4 x 3) when Model C-30s psychrometers were used at MD on DAE 120 and MA on DAE 124, and four repeated measurements across four treatments and three replications (4 x 4 x 3) when Model 84-3vC J.D.J. Merrill Specialty Equipment, Longan, UT, were used at MD (DAE 96, 106, 111, 113, 124) (i.e., means based on n = 36 or n = 48, respectively). Vertical bars are 1 SE of replication means (i.e., n = 3). Symbols in legend, source of variance, and results from ANOVA same as described in Fig. 1. Regression of on _W(PSY) (i.e., rate of change in osmotic potential; ) from anthesis until soft dough for fully expanded sunlit flag leaves of (c) spring wheat. Summary statistics for a linear regression are as follows: N, number of observations; R², coefficient of determination; S_y/x, SE of y given a value of x. The above illustration was derived from measurements from as many as 312 leaves.