Fig. 4.

Transmittance and reflectance spectra of the abaxial side of a N. paradoxa corolla. a Two transmittance spectra measured with an integrating sphere (T _ab) together with the average (${\overline{T}}_{\text{ad}}$) of the two transmittance spectra measured from the adaxial side (Fig. 2a). b Two reflectance spectra measured with an integrating sphere (R _ab; blue from a vein area, red from an area in between veins) together with reflectance spectra calculated for illumination from the abaxial side using the reflectances and transmittances of the various layers. The spectra were calculated with scattering parameter values 0.0, 0.1 and 0.2 of the unpigmented layer. The reflectance spectrum calculated with scattering parameter $S_{\text{u}}^{\ast }$ = 0.0 yields the averaged (measured) adaxial reflectance (${\overline{R}}_{\text{ad}}$); see text