“A tight ligature, by compressing and obstructing the passages through which the nutritive fluid has to pass, causes the formation of a similar swelling above the line of stoppage. You may have seen a sapling, bound too tightly to the stake intended for its support, strangled by its own growth if the gardener has forgotten to loose the band in time. Little by little the trunk swells above this band, which is finally overgrown by the bark and even hidden within its substance. Indeed, it is not rare to find a tree with its trunk caught fast in a narrow passage, as for example in the crevice of a rock, and swollen above the obstacle into an unsightly excrescence. The stoppage of the sap in its downward course explains this phenomenon. “If the tree-trunk is not completely encircled by the stricture, if somewhere there is a strip of bark left free to serve as a passage, the nourishing juice takes this way to get around the obstacle, and so pursues its course to the roots. Then the tree continues to live. But if the barrier is absolutely insuperable, as in the case of an unyielding ligature or when the tree has been girdled, the sap cannot descend to the roots to nourish them; and with the death of these the end of the tree is not far distant. “An important lesson remains to be drawn from these details concerning the circulation of this nutritive liquid in plants. Henceforth, when we fasten a plant to its prop or supporting stake, we shall be careful not to tie the string too tight or else to loosen it at the proper time, since otherwise we should run the risk of strangling the plant and so causing its death.” CHAPTER XXIV TREE-PRUNING “Self-preservation is the first law of a tree’s life, and next to that the preservation of its species, which is to be perpetuated by means of seeds. All this is perfectly natural, for no posterity would be possible to the tree unless its own existence were maintained in the first place. Accordingly the tree lives first for itself, accomplishing this object by covering itself with buds that develop into branches covered with leaves. It is indeed on the leaves that the fundamental principles of the plant’s life are based; it is in their substance that, with the sun’s help, the descending sap is elaborated, this sap being the nutritive fluid, the life-blood as it were, of the vegetable organism. The propagation of the species comes next in importance. This duty devolves on the flower-buds or those that blossom and produce fruit, in the center of which are the seeds.