Tracheid anatomy changes as responses to changing structural requirements of the tree

Summary After determining growth stresses at 10 positions around the periphery of the stem of a bent, 22 years old conifer (Pinus radiata), morphological details, density, increment rate, and strength were recorded for wood from each position. The trend of average microfibril angle exhibited a strong inverse relationship to the gravitationally induced strains at each position on the periphery, and correspondingly influenced the strength properties of the tissues there.The intensity of growth-stress generation was closely related to variations in microfibril angle, but not to lignin content. Together with changes in rate of differentiation, each was related to externally induced strains. It was concluded that the strains stimulated corresponding morphological controls of the differentiating tissue. Thus they modulated structural responses of the bent tree at all positions around its periphery, and so developed efficiently integrated action to reorient the stem to a stabilized vertical position.Similar conclusions resulted from a less comprehensive study on a straight tree of the same age and species. Further, somewhat compatible published data on growth stresses and property relationships in a large number of eucalypts indicated that the conclusions drawn from the detailed study of the bent Pinus radiata tree were generally applicable to other trees and species.The authors wish to acknowledge the valuable assistance of the Division of Mathematical Statistics, CSIRO, and particularly Miss N. Ditchburne for advice on sampling for the morphological studies, and for extensive calculations of results. In addition they are most grateful to colleagues J. E. Nicholson and G. Waugh for the field measurements of growth stresses, and to D. E. Bland for the lignin analyses.