Changes in the optical properties of cotyledons of Cucurbits pepo during the first seven days of their development

We recently discussed a method for measuring optical properties of light scattering and absorbing plant tissue ( Seyfried, Fukshansky & Schafer, 1983 ). This method has been used to measure the changes in optical properties of cotyledons between 360 and 1000 run during the first 7d of development. The seedlings were either etiolated or grown under continuous white light, the latter either herbicide‐treated (SAN 9789 = Norflurazon) or untreated. Some of the observed changes in seedlings grown under white light are due to chlorophyll accumulation. This accumulation leads to an increase in absorption coefficients at all wavelengths except in the 750 to 850 nm region. Reflectance, transmittance, and the scattering coefficient decreased markedly. Other changes seem to be independent of light conditions since they occur in much the same way under all treatments. These are a generally decreasing reflectance and scattering coefficient and an even stronger decrease of reflectance from the upper face of the cotyledon as compared to the reflectance from the lower face, in particular in the blue region of the spectrum. The observed changes are discussed in terms of light gradients and the resulting problems for in vivo spectroscopy.