Morphology and histochemistry can be used to distinguish between libriform fibers and fiber tracheids in tension and normal wood of red (Acer rubrum L.) and sugar (Acer saccharum Marsh.) maple. Utilization of a new differential staining method using safranin and astra blue dissolved in ethyl alcohol and an ultraviolet illumination technique (355-375 nm excitation) provides an effective method to distinguish between these fibers in microtome sections. Observations of the morphology of these tissues and their histochemical analyses were made using light and scanning electron microscopy. The Mäule reaction indicated less syringyl lignin in secondary walls of tension wood (outside of the G-layer) than in normal wood. Libriform fibers do not fluoresce in UV light in the wavelengths used, although fluorescence was observed in some of the cell corners, probably due to the presence of guaiacyl lignin in the cell corners. In normal and tension wood of both species, libriform fibers occur in interrupted wavy bands, have larger lumens than fiber tracheids, and intercellular spaces are commonly present
