Note 151 — Chapter III · THE RATE OF GROWTH (continued 2)

I had not received, when this was written, Mr Douglass’s paper, On a method of estimating Rainfall by the Growth of Trees, Bull. Amer. Geograph. Soc. XLVI, pp. 321–335, 1914. Mr Douglass does not fail to notice the long period here described; but he lays more stress on the occurrence of shorter cycles (of 11, 21 and 33 years), well known to meteorologists. Mr Douglass is inclined (and I think rightly) to correlate the variations in growth directly with fluctuations in rainfall, that is to say with alternate periods of moisture and aridity; but he points out that the temperature curves (and also the sunspot curves) are markedly similar.