Some Observations on the Growth in Thickness of Trees, especially with Regard to that of Cryptomeria japonica, DON.

1. Thickness of annual rings of trees in succeeding years is not uniform.2. Wild-grown trees in the woods have a long young stage of growth in thickness with thin annual rings, and show a very complex type of growth. Many planted trees, or trees growing in open stand are, however, characterized by short young stage of growth in thickness and show a simpler type of growth.3. Though radial curves of thickening growth show certain irregularities, they may be reduced to a form, which follows the formula R2=PXr, where r and P are variable numbers, the value of the former determining the type of the curve, and that of the latter, the inclination of the curve.4. The most general type of radial curves is the case when r=1, that is, R2=PX or R=√PX, which is the parabolic curve. In this case, the area of wood in cross section produced every year is constant. Large and old trees which I could hitherto observe showed the parabolic radial curves.5. Thickness of annual rings produced in the same year varies according to the height. In Cryptomeria, the maximum is at a height of between 1-7m., whence it decreases upwards and downwards.6. Though several authors found the close relation between the amount of precipitation and the growth in thickness of trees, I could not find any remarkable coincidence in this relation in Japanese trees, except some extreme cases.7. Length of tracheids in the wood of Cryptomeria varies with age. The rate of increase is greater in younger part, and becomes smaller gradually, until the length reaches the maximum at the 150-200th annual ring, and from this point it decreases very slowly outwardly. In Chamaecyparis, this maximum length continues through succeeding rings.8. Length of tracheids also varies according to the height. At the level between 3-11m. it has the maximum value, and decreases from this point upwards and downwards.9. In Cryptomeria, radial diameter of tracheids in cross section in one and the same annual ring has its maximum at some distance from the beginning of spring wood, passing outwardly to the compressed summer wood elements with the minimum diameter.10. Area in cross section of tracheids of these two coniferous trees also varies with age and height. The mode of variation is similar to that of length.11. Height of ray tissue of coniferous wood, in terms of number of cells, varies in the same way with the variation of length and area of tracheids, with regard to age and height.12. In Cryptomeria each cell of ray tissue has vertical height of 20μ (in average) throughout all parts of the tree.13. In dicotyledonous wood, there is the change of dimensions of xylem-elements according to age, though it is not so marked as in coniferous wood.14. Relative quantities of different xylem-elements change in different annual rings, in the case of Quercus.15. From these facts, we may conclude that the size of xylem-elements changes considerably in different parts of the tree. For the diagnostic purpose of different kinds of wood, it will be dangerous to adopt the dimensions of xylem-elements, without considering age and height of the wood, from which these elements are taken.