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The attenuance (apparent absorbance), angular distribution of transmitted light (scattering) and reflectance of paradermal sections of Camellia leaves were measured spectrophotometrically and the data for the palisade and spongy tissues were compared. Attenuance in tissues could be expressed by Beer's law only for wavelengths of strong absorption. At 680 nm, the apparent extinction coefficient of chlorophyll (e) for the spongy tissue was about 1.4 times that for the palisade tissue. The larger e for the spongy tissue is attributable mostly to the more effective increase in the pathlength of light due to scattering at the interfaces between the air space and cells because the difference between e for the two tissues was minimized by infiltration of the air space in the tissues with a medium whose refractive index was similar to the index of the leaf cells. Scattering was larger for wavelengths of weak absorption, and the relative increase in attenuance caused by elongating the optical pathlength was even more prominent. Based on these data, we report an ecophysiological discussion of the internal light environment of a leaf and the meaning of the differentiation of mesophyll into the palisade and spongy tissues.
Terashima et al. (Thu,) studied this question.