The Willstätter and Stoll theory explains leaf reflectance as critical or total reflection of light at cell wall‐air interfaces of spongy mesophyll tissue, and is based on observations of the spectral properties of leaves in the visible wavelengths. Our data, obtained in the 0.72 to 1.3 μm (reflective infrared) wavelengths, showed that unexpectedly high levels of reflectance occurred from palisade tissue and from dehydrated leaves that had collapsed internal structures.A modification of the Willstätter‐Stoll theory, termed the diffuse reflectance hypothesis, allows a satisfactory explanation of the observed spectral properties of leaves in the reflective infrared, as well as the visible wavelengths.