. Carnegie Institution of Washington publication. COLLECTION OF SECTIONS. 29 trees, shows so much greater agreement than the others that it has been used alone in drawing final conclusions. Its site was a small, poorly drained level space near the bottom of the valley. In this group there was no necessity of duplicating the Flagstaff records, and therefore small V-shaped cuttings were made at the edges of the stumps, only triangular pieces of wood giving the outer half cen- tury of ring-growth being brought away. These were the samples on which the value of the cross-identification was discove
. Carnegie Institution of Washington publication. COLLECTION OF SECTIONS. 29 trees, shows so much greater agreement than the others that it has been used alone in drawing final conclusions. Its site was a small, poorly drained level space near the bottom of the valley. In this group there was no necessity of duplicating the Flagstaff records, and therefore small V-shaped cuttings were made at the edges of the stumps, only triangular pieces of wood giving the outer half cen- tury of ring-growth being brought away. These were the samples on which the value of the cross-identification was discovered, as already described. Identical series of rings were observed in nearly every tree of the group. o c 30 25 20 1870 1880 Year 1890 1900 1910 = 15 10 0. V V :•• £ o FIG. 7.—Annual rainfall and growth of trees (Group V) at Prescott. Dotted line: rainfall. Solid line:growth. I Out of 67 sections averaging 50 rings each, only 6 gave any identifica- tion trouble. In 2 of these, 2 rings were lacking, but when allowance was made for this defect the identification was satisfactory. Another section had 2 extra rings, and another had 2 extra and 3 lacking. The other 2 sections proved especially puzzling and were finally omitted from the means. Of these 6 troublesome sections, the first 5 were very slow growers. Hence it would seem advisable not to use extremely slow-growing trees any more than is necessary. It may be urged that trees do not grow continuously at the slow or fast rate and that we can not tell how much of the change is due to rainfall. On the whole, how- ever, it seems advisable to exclude trees or parts of trees whose identi- fication is extremely difficult. The inner rings if well identified may be extremely useful in carrying back early records, as the slow-growing trees are likely to be among the oldest. The averages of 4 subgroups and the means of all the Prescott trees will be found plotted in figure 6. The curve of the fifth subgroup is giv
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