Rapid Measurement of Tracheid Cross-Sectional Dimensions of Conifers

An instrument has been developed that allows anatomical measurements to be made directly on the surface of a wood specimen that has received no special treatment other than hand smoothing of the surface. Average tracheid diameter and wall thickness are obtained with a maximum of speed and efficiency on a dual-linear traversing micrometer equipped with a Leitz Ultrapak microscope. Measurements made with this micrometer on cross sections of isolated earlywood and latewood of Douglas-fir were used to obtain estimates of wood specific gravity that were compared with actual values (obtained by the maximum-moisture method after extraction with alcohol-benzene). Formulas were developed for rectangular and elliptical lumen models on the basis of a restricted sample from two veneer logs. The formulas were tested against a second sample of 14 annual rings selected at random from the Forest Products Laboratory wood collection. The rectangular lumen model appears to be the more satisfactory of the two models. Tests of accuracy, using the rectangular lumen model, indicate that the predicted values for the second sample are within 0.02 unless a 1-in-3 chance has occurred. Estimates obtained for cell wall specific gravity substantiate the observation of Jayme and Krause that the values within a species vary within narrow limits only. Little, if any, difference was found between the cell wall specific gravity of earlywood and latewood in the swollen, extractive-free condition.

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