. Carnegie Institution of Washington publication. 136 THE CLIMATIC FACTOR AS ILLUSTRATED IN ARID AMERICA. yellow pine, one in New Mexico (the dotted line which we have already considered) and the other the curve for 217 trees in Idaho. The two curves were prepared in exactly the same way, and to both the corrections for age and longevity were applied according to the same mathematical processes. Nevertheless, they are almost diametrically opposed. ^Vllere one rises to a maximum the other is depressed to a minimum, and the oi)position is evident in practically every case. Between 1600 and 1700
. Carnegie Institution of Washington publication. 136 THE CLIMATIC FACTOR AS ILLUSTRATED IN ARID AMERICA. yellow pine, one in New Mexico (the dotted line which we have already considered) and the other the curve for 217 trees in Idaho. The two curves were prepared in exactly the same way, and to both the corrections for age and longevity were applied according to the same mathematical processes. Nevertheless, they are almost diametrically opposed. ^Vllere one rises to a maximum the other is depressed to a minimum, and the oi)position is evident in practically every case. Between 1600 and 1700 it is especially noticeable. During the next centurj', when climatic conditions were less extreme, the difference in the curves becomes less marked, and they run along together in a medial position. Then, in the nineteenth century, when drought was severe in New Mexico, the two curves are again in marked opposition. Moreover, the general trend of the New Mexican curve is downward, indicating that, on the whole, conditions during the past three centuries have liecome less favorable to the growth of the yellow pine in that region. The Idaho curve, on the contrary, tends upward, suggesting that conditions have there become more and more favorable. Much stress must not be laid on this last point, however, for the opposed trends may be due partly to errors in the determination of the corrective factors. The relation between the two curves of the yellow pine is susceptible of two inter- pretations. In the first place, it may indicate that rainy periods in New Mexico are syn- chronous with dry periods in Idaho; or, in the second place, it may mean that droughts are synchronous in the two regions, but that Ihe trees of New Mexico, growing in a warmer, drier region than the others, are stimulated by long winters, heavy snowfall, and late, moist springs, while those of Idaho are hindered by the same conditions. An examination of the rainfall of the two regions seems to confirm the first
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