Fig. 9. Spectral and reflection-polarization characteristics of a leaf of a Ficus benjamina tree (Ficaceae) as functions of the illumination conditions in the open. The leaf was mounted in front of the camera on a horizontal rod (holder), which rotated in a horizontal plane around a vertical axis together with the camera (insets I1 and I2). The solar elevation was _S=55°, and the leaf was illuminated by direct sunlight (parts A, C, E and G) or shaded with a small screen that just occluded the sun and exposed the leaf to the full clear sky (parts B, D, F and H). In the small rectangular left and right window, the leaf blade is approximately horizontal and vertical, respectively. Inset I3 shows the four different horizontal directions of view of the camera with respect to the solar azimuth. ASM, antisolar meridian; SM, solar meridian; EPSM, eastwardly perpendicular to the solar meridian; WPSM, westwardly perpendicular to the solar meridian. Column 1 shows colour video pictures of the leaf. Column 2 shows patterns of the degree of linear polarization of the leaf measured by video polarimetry at a wavelength of 450nm (blue). Column 3 shows patterns of the angle of polarization (measured from the vertical) of the leaf at a wavelength of 450nm, where the dominant (average) electric field vector alignment of the leaf blade is represented by a solid arrow, and the standard deviations are represented by broken arrows.

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