DEPARTMENT OF BOTANICAL RESEARCH. 73 



The second object of the year's study — the mathematical measurement of 

 changes of climate — has been accomplished by means of further investiga- 

 tion of the rate of growth of old trees. Several thousand stump analyses 

 gathered from various parts of the United States by the U. S. Forest Service 

 were most courteously placed at the disposal of the Carnegie Institution of 

 Washington by the Forester. Mr. H. S. Graves. From these a series of 16 

 corrected curves of growth have been prepared. They show the growth of 

 the trees during a period of from 300 to 1,000 years and prove that it has 

 varied greatly from time to time. The variation is cyclic in character, and 

 is of such a nature that it can not be due to fires or other accidents, and 

 must apparently be of climatic origin. The full interpretation has not yet 

 been made, since different trees are stimulated by different conditions, some 

 responding to warmth, others to abundant moisture, and still others to other 

 conditions, according to the habits and habitat of the species. Hence, before 

 the climatic conditions of any given part of the country during past centuries 

 can be ascertained exactly, it is necessary to determine the precise conditions 

 which stimulate or repress the growth of the various species. This can be 

 done by comparing a series of annual measurements for the last 50 years, 

 more or less, with the nearest available meteorological records. This com- 

 parison has been made in the case of the yellow pine by Prof. A. E. Douglass 

 at the request of Mr. Huntington, and in the case of the Sequoia gigantea 

 by Mr. Huntington himself. In 15 other cases, however, it must be deferred 

 until a series of measurements of annual growth can be secured, the meas- 

 urements furnished by the Forest Service having been made by decades. 



The most important work of the year was a further study of the Big Trees 

 of California. In addition to the 250 measurements of stumps made last 

 year, about 650 more were made, a total of nearly 900 measurements upon 

 450 trees. The total number of individual readings is in the neighborhood 

 of 130,000, while the number of rings actually counted now amounts to 

 about 1,300,000. The work of tabulating this mass of figures is well under 

 way, and will be completed before the end of the calendar year. It will 

 enable us to draw a curve showing in detail how the climate of California 

 has varied for the past 3,000 years ; and this curve will possess a degree of 

 accuracy far greater than has hitherto been supposed possible. It will fur- 

 nish a mathematical key to the past climate not only in America, but of the 

 eastern hemisphere; and it will probably be one of the important steps 

 toward the prediction of climatic changes which may occur in the future. 



To facilitate the obtaining of measurements of tree growth in remote 

 regions, a boring machine was constructed and was given a thorough trial in 

 California. It worked well, save that a further device for clearing shavings 

 is necessary. When this is added the machine will be a valuable aid in pro- 

 curing sections of wood in the form of horizontal cores from trees in places 

 where no freshly cut stumps are available. 



The pursuit of the third object of the year's work, the inquiry into the 

 possible relation of climatic changes to other types of phenomena, was at- 



