Page:Climatic Cycles and Tree-Growth - 1919.djvu/72

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IV. DETAILS OF CURVE PRODUCTION.

PREPARATION OF RADIAL SAMPLES.

Form of sample.—Nearly all of the 230 trees used in this investigation are represented by portions preserved in my collection. Wherever possible the entire section, 1 to 3 inches or more in thickness, was brought to the laboratory for examination. Unless the section was light and easily handled, it was found convenient to cut from it a radial piece showing the complete series of rings from center to bark. Naturally the enormous trees of the sequoia groups could be obtained only in radial form. The paper rubbings from Oregon and the small cuttings of the Prescott and second Flagstaff groups were also of this type. Hence the radial sample is regarded as the usual or type form in which the material appears in the laboratory. If the original section was small the radial piece appears as a bit of wood cut across the grain, square or triangular in cross-section and a foot, more or less, in length.

Method of Cutting.—The partial radials, such as used in the Prescott group, were secured from the stumps in place by making saw cuts at the edge of the stump in two directions, meeting a few inches below the surface. In this manner a piece of wood in the form of a triangular pyramid was secured and was sent to the laboratory. The radials of the sequoias were cut altogether from the tops of stumps or from the ends of logs that lay on the ground. From the manner in which the trees were cut down it was usually possible to get a clear surface of stump or log from the bark on one side to somewhat past the center where the under-cut had been made. After a minute examination of the surface exposed, a radius was selected which would give the greatest freedom from fire-scars and other irregularities of ring distribution. Two lines about 8 inches apart were drawn with blue chalk along this radius. Then two men with a saw 8 to 14 feet in length made a slanting cut on one of the lines of sufficient depth and in the right direction to meet a similar slanting cut from the other chalk line. In this way a long piece of wood of V-shape in cross-section was obtained, extending from the center to the outside and giving the full ring record.

In sequoias recently felled this cutting of the radials was extremely easy, but many of the sections obtained were from stumps which had been standing and weathering for 25 years and in one case 43 years. The exposure carbonizes the top of the stump and makes it extremely brittle and difficult to cut; small pieces break off and wedge the saw. Thus it often becomes a very difficult task to extract the radial section. The pieces into which the radial section breaks are marked for identification immediately, photographed and listed in notebook, and then carefully packed for shipment. On arriving at the laboratory, they are pieced together with the greatest care and then glued together in groups, making the entire radial section a series of convenient pieces about 2 to 3 feet in length.