III. COLLECTION OF SECTIONS.
The material upon which the discussion of climatic cycles and tree-growth is based has been derived from 230 trees collected in the 15 years from 1904 to 1918. The regions drawn upon comprise chiefly Arizona with its yellow pine, the Baltic drainage area of north Europe with its Scotch pine, and the high Sierras of California with their great sequoia. Two small collections come respectively from the northeast and northwest coast of the United States. The collections have been made in small, convenient groups as opportunity offered, to each of which a name has been given which will appear below.
The relative dimensions of the various groups may be expressed in terms of the number of measures of rings. In the first Flagstaff group there were about 10,000. In the second Flagstaff group of 1911 only a few hundred. The Prescott groups included about 4,000; the 9 European groups about 9,000. The Vermont group had between 2,500 and 3,000, and the Oregon group about the same. The first collection of sequoias in 1915 had about 25,000 measures and the collection in 1918 embraced about 22,000.
Throughout the whole study it was desired to get as long records as possible and old trees were therefore selected. In nearly every case this meant large trees also. Apart from this no special selection of trees was made at any time, save only in the Christiania group, in which so many of the logs showed a "complacent" habit, with long successions of equal rings rather large in size, that some effort was there made to find the logs which showed variations in ring-size. A complacent ring-record without doubt means that the environment of the trees was well adapted for its best development.
THE FIRST FLAGSTAFF GROUP OF TWENTY-FIVE SECTIONS.
The plan of using tree-rings for the general purpose of a check on astronomical and meteorological phenomena was first formulated in 1901. The first measurements were made in January 1904, on a huge log in the yards of the Arizona Lumber and Timber Company at Flagstaff. This method of measuring was extremely inconvenient and the succeeding 5 sections were cut from logs and sent to town for more careful examination. Hence the exact location of these first 6 was never visited. The remaining 19 trees were selected in 1906 by myself in the forest while the logs were yet lying near their stumps, and I was able to mark on each section the points of the compass and otherwise describe the location. The measurements were completed in 1907 and published in the Monthly Weather Review of June 1909. They had not been subjected to cross-identification and, when the value of this