The hardest, and heaviest woods come from the hotter climates; the only exception is the pine, which thrives considerably better, and furnishes heavier timber, when it has grown in colder regions, or upon high mountains.
Trees grown on northern slopes furnish lighter timber than if grown on southern or western. The soil has great influence upon the width of the yearly rings, and from this we are able to come to a conclusion in regard to the specific weight. In the fir and larch trees the wood is heaviest when their rings are smallest.
The difference in the strength of timber between the south and the north side is attributable to the grain being closer on the north side, as the sap does not rise in the same proportion as upon the south. In forest-grown wood the difference is almost imperceptible, as the sun cannot act upon the trunk of the tree; in open-grown timber, the difference is really perceptible. It is well known that all woods do not lose strength by being open grown, or, in other words, that the south side is not always weaker than the north; that theory only applies to the coniferæ species. In ash it is the opposite, as the south side is the strongest. In soft-wooded trees, as the acer species, the difference is not perceptible, as the annual rings, and the intervening cellular tissues, are so close akin as to render the wood so compact in its grain that there is no difference in its strength. The coniferæ species, or the pines, are the only classes of woods that are stronger on the north side than on the south: it is well known that the difference originates in the wood being more open in the grain on the south side than on the north.
An influence upon the specific weight is exercised by the resin, and the die, which are contained in the interior of the wood. On level dry ground, or deep sandy soil, we find the fir beautifully red inside; but when we look at it on lias soil, it shows broad yearly rings, and hardly any colour at all. The larch tree, again, in such soil, develops itself well with a rich colour. The cause for these appearances must therefore rest with the chemical condition of the soil, and its effect upon the individuality of the fir: it is probably the nature of the soil that causes the difference of character between Honduras and Spanish mahogany; Honduras being full of black specks, and Spanish of minute white particles, as if it had been rubbed over with chalk. Oaks generally furnish good timber when grown slowly in dry ground, whilst those from wet soil appear comparatively spongy; similar results are obtained with other trees.