Fluorescence microscopy for measuring fibril angles in pine tracheids.

—Observation and measurement of fibril angles in increment cores or similar small samples from living pine trees was facilitated by the use of fluorescence microscopy. Although some autofluorescence was present, brighter images could be obtained by staining the specimens with a 0.1% aqueous solution of a fluoro­ chrome (Calcozine flavine TG extra concentrated, Calcozine red 6G extra, rhodamine 6G, rhodamine 6GD extra, or a succession of flavine and rhodamine). Staining for 2-5 min followed by a 5-10 sec washing in distilled water and drying 15 min at 190-195°C prepared radially split surf aces of specimens for microscopic obser­ vation with ultraviolet light. Measurement of fibril angles, im­ portant for the determination of wood strength and the properties of its pulp, was made with a protractor eyepiece. Photomicrography was feasible also, and the need of preparing microtome sections was obviated. INTRODUCTION The strength and longitudinal shrinkage of wood and the prop­ erties of pulp are greatly influenced by the angle at which fibrils lie with respect to the longitudinal axis of wood fibers. In summerwood fibers, these fibril angles have been found to vary widely, from near parallelism to 45° or more (Pillow, et al, 1953). The smaller angles, less than 10°, have been found to be associated with the favorable strength and dimensional stability of such wood as that of the southern yellow pines and the good tearing strength of kraft paper made from these woods. On the other hand, larger fibril angles, 20-45°, contributed particularly to poor stiffness and excessive longitudinal warping in lumber and to inferior tearing strength of kraft paper. For these reasons, the sizes of fibril angles in summerwood of yellow pines are recognized as an important index of wood and paper properties. Such an index has a particular value in forest products research, since it provides an estimate of the intrinsic prop­ erties of sound and clear wood on the basis of fiber structure. Through the determination of fibril angles (together with wood density), it is possible to obtain a reasonable evaluation of those properties for superior or elite phenotypes and for hybrids. The 1Maintained at Madison, Wis., in cooperation with the University of Wisconsin. STAIN TECHNOLOGY, VOL. 30, No. 5, SEPTEMBER 1955