240 



THE RATE OF GROWTH 



[CH. 



data are reduced, as before, to moving averages of 100 years, but 

 without further correction. The agreement between the growth- 

 rate of these pines and that of the great Sequoias during the same 

 period is very remarkable (Fig. 74). 



We should be left in doubt, so far as these observations go, 

 whether the essential factor be a fluctuation of temperature or an 

 alternation of drought and humidity; but the character of the 

 Arizona chmate, and the known facts of recent years, encourage 

 the behef that the latter is the more direct and more important 

 factor. In a New England forest many trees of many kinds were 

 studied after a hurricane; they shewed on the whole no correlation^ 



1440 



CQ 



Fig. 74. Long-period fluctuation in growth of Arizona redwood (Sequoia), from 

 A.D. 1390 to 1910; and of yellow pine from Calaveras County, from a.d. 1620 

 to 1920. (Smoothed in 100-year periods.) 



between growth-rate and temperature, with the remarkable exception 

 (in the conifers) of a clear correlation with the temperature of 

 March and April, a month or two before the season's growth began. 

 In a cold spring the melting snows and early rains ran off into the 

 rivers, in a warm and early one they sank into the soil * ; in other 

 words, humidity was still the controlling factor. An ancient oak' 

 tree in Tunis is said to have recorded fifty years of abundant rain. 



pp. 321-335, 1914; nor, of course, his great work on Climatic cycles and tree- 

 growth, Carnegie Inst. Publications, 1919, 1928, 1936. Mr Douglass does not 

 fail to notice the long period here described, but he is more interested in the 

 sunspot-cycle and other shorter cycles known to meteorologists. See also (int. al.) 

 E. Huntingdon, The fluctuating climate of North America, Geograph. Journ. 

 Oct. 1912; and Otto Pettersson, Climatic variation in historic and prehistoric 

 time, Svens^M, Hydrografisk-Biolog. Skrifter, v, 1914. 



♦ C. J. Lyon, Amer. Assoc. Rep. 1939; Nature, Apr. 13, 1940, p. 595. 



