PRELIMINARY STUDIES ON THE YELLOW PINE. 17 



could be identified at once in terms of the rings at Prescott; the narrow 

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

 compressed series from 1879 to 1885 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 eleva- 

 tions approximating the elevation at Flagstaff have a considerably 

 closer resemblance to the Flagstaff sections than do those growing 

 at lower altitudes. 



Cross-identification and climate. The process of cross-identification 

 appears to be applicable to areas far removed from one another, 

 but as the distances increase the resemblances between tree-growth 

 records decrease, due to climatic differences. The correspondence 

 between trees in different regions thus becomes a test of climate and 

 we note a possible field for the application of this process in the delinea- 

 tion of similar climatic areas or meteorological districts. It seems to 

 the author that in this way the growth of vegetation may easily be 

 made of fundamental value in practical meteorology. 



MONTH OF BEGINNING ANNUAL MEANS. 



It is evident that it must take some time for the transmutation of 

 rain into an important part of the organic tissue. There is evidence, 

 as will be shown later, that the summer rains often have a prompt 

 effect. The winter precipitation, however, is necessarily more remote in 

 its action. Much of the first growth in the spring must come from the 

 melting of the autumn and winter snows. It seems reasonable, there- 

 fore, to consider any snowfall as applying to the following yearly ring. 



At Flagstaff the precipitation of November is almost always in the 

 form of snow, and therefore that month should certainly be considered 

 as falling after the arboreal New Year of tliat locality. In view of the 

 uncertainty as to the exact month when the precipitation begins to 

 have an influence upon the growth of the following season, and of 

 probable variations in different years, it seemed wise to test the matter 

 by a purely empirical method. The annual rainfall was ascertained 

 for yearly periods beginning (1) with July 1 of the preceding year, 

 (2) with August 1, and so on to (9) with March 1 of the current year. 

 Another method involved a separating of the summer rains, one-half 

 to apply on each adjacent winter, while a final method involved a 

 simiLar division of the winter rains. This was done for 12 years at 

 Flagstaff and 43 at Prescott. Part of the Flagstaff curves are given 

 in the lower portion of figure 4, where the rainfall can be compared 

 with the growth of the trees. The curves plotted from these tests were 

 found to have substantial disagreements, although of course the 

 smoothed curves of all of them would be practically identical. A 

 comparison of the growth of the tree with these various curves showed 



