Repository: UIHistories Project: Board of Trustees Minutes - 1886 [PAGE 295]

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Where two numbers are given in a column the first shows the water in the inner portion, and the second in the succeeding ring of growth.

Trees. P r P r cent. Diam. of ew a tcent. of ewater.— er — In. Heart. Bap. 43105 44.67 42.29 142.75 44.30 46.0042.30 43.80 41.92 40.85 41.18 1 31.36 33.46 38.18 45.35 38.95

H e w e s ' Virginia Crab, No. 1 H e w e s ' Virginia Crab, No. 2. Wilson's Sweet B o x Elder B o x Elder Box Elder Soft Maple

In the spring some of these trees would contain a greater per cent, of water, but I have no figures for the amount. What has now been given may be a surprise to many, and the query would hardly be unnatural, "Why do not all the tree trunks burst when exposed to a freezing temperature?" If, however, the internal wood is sound—rotten wood soaks up great quantities of water—and the spring activities of the roots have not commenced, it is not likely that the trunks of any trees will burst by the swelling of ice formation ; whether or not the shrinking of the tissues by cold without concurrent freezing is with us ever sufficient to' cause the longitudinal cracks we observe, after the manner of shrinking by drying, I cannot tell. Probably the bark may sometimes part through this cause. The tendency to such cracking by the change in size as the temperature decreases is just as certain as by the change through drying by heat. The only question is as to the amount of contraction by such cold as we have. Probably no trees ever burst until the thermometer marks zero or below, and then usually when the heart is more or less rotten, or after the roots have started to absorb quantities of water from the soil, as in spring-time. But this cracking open of the bark, or the latter and the wood,, does, as stated, comparatively little injury. It simply makes a bad wound without in the least otherwise destroying the vitality or healthfulness of the tree. I shall, therefore, only add an explanation of the crack so commonly occurring on the south side, or that most exposed to the sun. If this splitting of the trunk can be properly compared to the bursting of a water pipe, how can it be that the points of the compass have anything to do with it. The rupture of an iron tube always occurs in the weakest place, and no amount of thawing and freezing on one side, with the other less subject to such changes,, can make any difference in the result. Action and reaction are equal, pressure southward means equal pressure northward, and so of east and west. Now so far as the outer layer of bark is concerned the south side is the weakest, because of the drying effects of the sun—cracks, always being more numerous here than elsewhere—and this difference in strength, slight as it is, should be sufficient to cause the Ind—19