Repository: UIHistories Project: Board of Trustees Minutes - 1886 [PAGE 290]

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284 is in no sense a scald produced by heat. The same thing can be artificially brought about by inoculation with blight bacteria—has been done—and the inoculations succeed as well on the north as on the south side. But the influence of the sun upon the outer bark of trees is well known to every one who has frequented the woods without a compass, and to every one else who has been sharp in his observations. The outside corky envelope, old and dead, is much more deeply cracked and furrowed on the south than on the north side, and it does not usually take lon^ to discover if one looks, especially in early summer, that many of these cracks extend to the living cells, which are thereby exposed to the contagion of blight. So long as the bark of young trees remains smooth, and is otherwise free from wounds, we do not find this affection of the trunks. When trees lean from the sun the rays of heat fall more nearly at right fugles to the surface, and are thus more effective in destroying the elasticity of the outer protecting bark. Bains, too, may more readily wash fine material into the cracks, and thus in numerous cases be the means of infection. Beginning «from without, it is not very uncommon for blight to be confined to the living, cellular layer outside of the bast or fibrous layer of inner bark. In case the cambium layer (inside the bast) is not invaded, new bark may be formed and the tree saved, as already said. Evidently, keeping the tree erect or leaning to the southwest, and providing a shield of some kind winter and summer, to protect the bark from drying and cracking, are protective measures, and they are the best we have. We now pass to the fourth cause of injury, namely, freezing; and shall enter more into detail. The injury due to frost, so far as the trunks of our trees are concerned, is of two kinds. In one case the wood and bark is split so as to gape open while frozen, though the crack may be closed after warm weather comes again. Sometimes only the bark thus cracks, and then there is left a more or less considerable wound, which becomes much more evident as the new layer of growth pushes out the torn edges. These cracks are much more frequent on the south or southerly side, but sometimes are otherwise located. Numerous kinds of trees are known to suffer in this way, and among others the following have, in my observation, been quite commonly cracked: apple, sweet cherry, plum, box-elder, hard maple, butternut, iron-wood (Carpinus), chestnut; and occasionally the black walnut, white willow, tulip poplar, oaks and linden have been seen similarly burst. No doubt the list can be greatly extended. But this form of injury is not nearly so destructive as the next to be mentioned. Trees are rarely severely checked in growth, and probably never, through this cause alone, are killed, though the wound may be deep and long and slow to heal. The second form of injury by frost is the separation of the bark from the wood, occurring for the most part near the ground, and also usually most common, on the side next the sun; but very often, much more so than in the former case, seen on any side or en~