Figure 3.

Coloration of the abaxial side of R. acris petals and pigmentation. (a) A small area observed with bright-field illumination and focus at the lower epidermis. (b) Dark-field illumination with focus at the mesophyll layer; scale bar: (a,b) 50 µm. (c) Reflectance spectra measured from 5–10 µm sized areas with the MSP of the lower and isolated upper epidermis and a boundary area of mesophyll cells. (d) Normalized absorbance spectra measured with the MSP from an isolated upper and lower epidermis, together with the spectrum of β-carotene in hexane. (Adapted from http://omlc.org/spectra/PhotochemCAD/data/041-abs.txt.)