CYCLES 



125 



Coast zone: — Cycles 17 and 20 years are largely lacking. The 10 

 and 11 year cycles are stronger here than in the other zones, but the 

 23-year cycle is the strongest in this zone. 



Zone summary — The characteristics of the three zones are brought 

 out in the following list : 



Sequoia cycles — The above summary deals almost entirely with 

 the yellow pine; for comparison the cycle analyses of some 32 sequoias, 

 from 1400 on, have been combined into one arcigram which agrees 



7 B 9 10 II 12 13 14 IS 16 17 16 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 39. 



Cycle length in years 

 Fig. 16 — Sequoia cycles 



with the pines in the coast zone in giving prominence to cycles of 10, 

 11, and 14 years, but differs from them in having a very prominent 

 20-year cycle with lowered emphasis on the 23-year cycle. This 

 includes the entire list of sequoias in the General Grant Park region 

 without selection of any kind, and indicates more resemblance to the 

 Arizona reaction than appears in the pines of the same area. 



SOLAR RECORDS IN TREE-GROWTH 



Historical confirmation — From the start the sunspot cycle was 

 sought in the Arizona pines, and during large portions of their growth 

 it seemed perfectly evident, but for scores of years near 1700 it failed 

 entirely; in 1914 the writer very nearly gave up the idea that the trees 

 show it. In 1919 (Volume I, p. 102) the cycle record was given with 

 the statement that from 1660 to 1720 the sunspot curve " flattens out 

 in a striking manner," and again, "the sequoias show strikingly the 

 flattening of the curve from 1670 or 1680 to 1727," and again, "it 

 seems likely that the sunspot cycle has been operating since 1400 a. d., 



