A differential staining method to identify lignified and unlignified tissues.

We investigated the use of safranin O and astra blue dissolved in ethyl alcohol as differential stains to distinguish between lignified and unlignified tissues in microtome sections of tension and normal wood of sugar and red maple. Normal wood was used as a control for the histochemical analysis. Lignified and unlignified tissues were found in the same section for both tension and normal wood of each species. These results were confirmed in unstained samples using ultraviolet light. Unlignified libriform fibers were detected using both techniques. Libriform fibers did not fluoresce in UV light, although fluorescence was observed in some of the cell corners. The astra blue in ethyl alcohol and the UV wavelength we used differentiated syringyl from guaiacyl lignins. Ethyl alcohol solutions of these dyes provide an effective and reliable method to distinguish lignified and unlignified tissues.