Fig. 5. Radiation-efficiency (e) as a function of the daytime vapor pressured deficit of the air (D). Information includes data from this study and data gathered from the literature. Data of this study and Goyne et al. (1993) are for barley and the remaining information is for wheat. The unpublished data are for spring wheat cv. Hank and winter wheat cv. Falcon. The arrow indicates an outlier excluded from the regression (see text for explanation); if included the regression is e = 1.79 – 0.47D (r² = 0.50, n = 23).