This section is from "The Horticulturist, And Journal Of Rural Art And Rural Taste", by P. Barry, A. J. Downing, J. Jay Smith, Peter B. Mead, F. W. Woodward, Henry T. Williams. Also available from Amazon: Horticulturist and Journal of Rural Art and Rural Taste.
"That is a fine piece of Oak," remarked an experienced and very intelligent person the other day while looking at the section of one of the old principals of the chapel roof of Hampton Court; "how fast it grew on THE
SOUTH SIDE!". "How do you know that to have been the south side?"was the reply. " Oh I you will always find that it is the south side of an Oak tree which grows fastest." It was not the first time that such an assertion had met our ears; but we had imagined the opinion to be confined to a few very old-fashioned gardeners and woodmen; in this we were mistaken. Let us then endeavor to disabuse the horticultural and arboricultural mind of what is surely a great error.
Timber is formed by the action of leaves, and in no other possible manner. That is a law to which there is no exception; and there we take our stand. The quantity of timber will be in direct proportion to the area of leaves; that is to say, six leaves having a surface of twelve square inches will have as much timber-forming power as twelve leaves having the same surface. Such being the case, to say that a tree has always most timber on the south side is the same as saying that a tree has most leaves or a greater area of foliage on the south than on any other side. Is that true? Certainly not.
A tree grows near the north wall of a high house; on the side next the house, namely, the south side of the tree, there is least timber, while on the opposite or north side there is most. The following figure represents a circular wood, with four trees standing on its circumference at the cardinal points, the interior of the wood being crowded. At N the principal formation of timber will be on the north side of the tree; at W on its west side, and at E on its east side. If a tree grows singly, without any hindrance to its regular development, it will have the same quantity of foliage on each side, and the production of timber will be as uniformly concentrical as could be represented by successive circles drawn by a pair of compasses. In all these cases the excess of timber on the south side does not take place; no , doubt at the point s on the circle, which represents the south, most timber will be formed on the south side, but without any greater difference than will be found at E, N, and W. Now this we take to be an exact statement of what happens in the cases supposed; and if so, the popular notion to which we have alluded is disposed of.
The reason why there is most timber at N, E, W, and s on the above circle is, not that trees are exposed to one point of the compass more than another, but that the letters represent the outside of the wood. On that side branches form most abundantly, leaves are larger, and the roots have more space than they can have on the side next the interior of the wood. Most wood is formed at s because there is most timber-forming power in action there, not because it faces the south; as, indeed, is plainly shown at N, which has least timber on the south side. Let any one living on the south coast examine the trees that first catch the sea spray, and we will engage that he will find, without an exception - unless the sea spray is inoperative, as happens to Pinasters, Evergreen Oaks, and some others - that the smallest quantity of timber is on the south side. For there the branches are broken by gales, the buds are nipped by salt, and the leaves are perpetually perishing under the influence of oceanic action.
Doubtless it often happens that the south side of a tree has most timber, owing to a variety of local causes, especially exposure to cold, cutting northerly winds acting during the spring upon their side. But it is evident that the excess of timber in such a case is not due to the aspect being southern, but to the impossibility of timber being formed on the northern side, owing to injury arising out of the causes we have mentioned. Were the injurious influences to proceed from the southward, then there would be most timber on the north side.
To some this little explanation may seem trifling; but even if the matter 1 itself deserved to be so considered, that can never be a waste of time which j establishes the minutest point of truth. In gardening most especially, where false inferences are so common and injurious, it is of the first importance to seize upon every opportunity of showing the difference between what is termed post hoc and propter hoc; that is to say, between an accidental occurrence and a necessary consequence. - London Gardener's Chronicle.