Verifying the Preston equation between the average of tracheid length and microfibril angle in Cupressus arizonica compression and opposite wood

In a conifer, an increase in tracheid length is usually accompanied with a decrease in microfibril angle of S2 layer (MFA). Preston proposed an equation relating these two features, quantitatively. However, this equation has less been verified in subsequent works. Hence, in this study, variation of tracheid length and MFA from pith to bark in compression and opposite wood of Cupressus arizonica was investigated and it was tried to determine the relationship between these two factors, quantitatively. Results showed that the tracheids are shorter and mean MFA is bigger in compression than opposite wood. Moreover, in both sides mean tracheid length increased from pith to bark while MFA decreased in the same direction. A strong and negative relation was found between the mean tracheid length and MFA in both areas which was of nonlinear type when compression, and compression and opposite wood together were concerned. Overall, Preston equation between these two anatomical features was verified.