ABSTRACT
This chapter describes techniques for obtaining composition data while retaining the sample in its original condition. The procedures used for reflectance or transmittance spectroscopy of intact plant materials are empirical, but once an equation has been developed for determining the concentration of a substance in plant tissue, subsequent measurements can be made in a matter of seconds. Absorption becomes a factor in specular reflectance only when the absorption is very high. When there is significant absorption in a distance equal to one wavelength of the radiation propagating into a material, the specular reflectance increases. The wavelength range for diffuse reflectance measurements on fresh plant tissue is determined by the spectral transmittance properties of water. Water has a minimum absorption in the green part of the visible, and there are several absorption maxima through the infrared.
