106 THE CLIMATIC FACTOR AS ILLUSTRATED IN ARID AMERICA. 



to 1867, when the rainfall record begins. Two others in the first group, with 40 and 

 41 rings, respectively, one in the second with 38 rings, and one in the third with 41, were 

 made use of, although they did not quite go back the necessary 43 years. The values of 

 the deficient rings were supplied by extrapolation and comparison. 



Of these five groups the first four were collected in the autumn of 1911, measured, and 

 their average curves drawn. While the comparison with the annual rainfall gave very 

 promising results, it was apparent that the agreement between growth and precipitation 

 increases as the location of the actual rainfall station is approached This sustained the 

 opinion of Mr. R. H. Forbes, Director of the Agricultural Experiment Station at the 

 University of Arizona, that rainfall in the mountainous region about Prescott is extremely 

 variable, and for individual years one point can not be judged safely from others. This 

 made it necessary to get some samples from nearer town. Mr. Hinderer, therefore, went 

 to the further trouble of finding some stumps which were near town, about a dozen in all, 

 from which the ten sections of the last group were cut. These ten show so much greater 

 agreement with the rainfall than do the others that they have been used alone in the final 

 conclusions. 



The chief feature of the Prescott series which places its results on a firmer basis than 

 any previous work is the cross-identification of rings between trees. The extent and 

 accuracy of this identification came as a surprise to the writer. After measuring the first 

 18 sections it became apparent that much the same succession of rings occurs in each, 

 and thereupon the other sections were examined and the appearance of some 60 or 70 rings 

 memorized. All the sections were then reviewed, and pin-pricks placed in the wood 

 against certain rings. Certain characteristics were noted as common to all, for example, 

 the red ring of 1896 is nearly always double, while the rings of 1884 and 1885 are 

 wider than their neighbors. The most conspicuous feature was a series of compressed 

 rings from 1878 to 1883, preceded by a very faint 1877 and then a long series of very wide 

 rings. 



Out of 67 sections averaging 50 rings each, only 6 gave any trouble at the start. 

 In two of these, 2 rings were lacking, but when allowance was made for this defect, the 

 identification of the remainder was satisfactory. Another section had 2 extra rings, and 

 another had 2 extra and 3 lacking. The other two sections proved especially puzzling. 

 It finally appeared fairly certain that one of them had the rings from 1879 to 1887 merged 

 into one, and the rings from 1890 to 1895 merged into one. The other had the rings for 

 1890 to 1895 in one and 1898 to 1900 in one. Of these six troublesome sections, the first 

 five were very slow growers. Hence it would seem advisable not to use extremely slow- 

 growing trees any more than is necessary. In objection it may be urged that the trees 

 do not grow continuously at the slow or fast rate, and we can not tell how much of the 

 change is due to rainfall. On the whole, however, it seems advisable to exclude trees, or 

 parts of trees, whose identification is extremely difficult. The inner rings, if well identi- 

 fied, may be extremely useful in carrying back early records, as the slow-growing trees are 

 likely to be among the oldest. 



The cross-identification of trees from the Prescott region was limited to an area only 

 10 miles long. It came as a surprise, then, to find that shavings from the Flagstaff sections, 

 such as are shown in Plate 4, could be identified at once in terms of the rings at Prescott. 

 The narrow ring of 1851 was at once seen to correspond to one in the Prescott series. The 

 dense series from 1879 to 1883 likewise had its counterpart at Prescott and formed the 

 portion of the sections which gave the most difficulties in identification. On the whole, so far 

 as can be judged without minute study, the Prescott trees from relatively high elevations 

 approximating the elevation at Flagstaff have a considerably closer resemblance to the 

 Flagstaff section than do those from trees growing at lower altitudes. The process of 

 cross-identification appears to be applicable to areas far removed from one another. Two 



