100 CLIMATIC CYCLES AND TREE-GROWTH. 



England show slight relation to the solar cycle. They show more 

 prominently other variations, which, taken between 1870 and 1900, may 

 have given rise to Lockyers 3.8-year period (1905, 1906). The full 

 tree record becomes more accordant on a 3.5-year period. In this 

 group there appears to be a slight relation to London rainfall of a 

 direct character, that is, the growth is larger with increased rain. 

 Naturally in such a well-cultivated region there may have been large 

 differences due to treatment of the soil, drainage, and so forth. The 

 other two European groups, one from Pilsen in Bohemia and one from 

 the north slopes of the Alps in southern Bavaria, do not show consistent 

 agreement with the solar variation. Yet the former shows a double 

 sunspot period which is illustrated below. 



Coming to the American continent, the Vermont group may also 

 be considered as growing in a wet climate. It shows a very strong 

 single-creasted solar period, but the maxima come 3 years early during 

 the last century. During the preceding century, when the trees were 

 younger, the tree maximum is only 1 year early. The rainfall in this 

 region shows the solar period also, but it is roughly inverted with 

 respect to the tree curve. The Oregon group must be considered as in 

 the wet climate of the temperate zone. It is near the Pacific coast and 

 has abundant rain or snow. The solar cycle is probably in it, but it is 

 not so conspicuous as other short cycles. When these trees are summed 

 up on the 11-year period, they show about 10 per cent total variation 

 with maximum and minimum coinciding with the Vermont group and 

 therefore anticipating the sunspot maximum by 3 years. 



The sequoias grow farther south and experience the heavy pre- 

 cipitalion of the temperate-zone winter combined with dry-climate 

 summer conditions that is, the summers are mostly clear, but have 

 occasional sharp local showers, often with lightning The tree-growth 

 shows a relation to the rainfall in the great valley below and therefore 

 we could expect some similarity to the Arizona pines. This does exist, 

 but the exact 11.4-year cycle shown in the pines is less evident in the 

 sequoias, though unmistakably there. The analysis of the long 

 sequoia record will be shown below. In it several cycles between 7 and 

 15 years predominate in places. The 11 -year period is plainly evident 

 through most of the record and for some centuries is the predominant 

 cycle, but for long periods other slightly differing cycles, such as 10 

 years, 12.6 years, or 13 years, are more evident. It is as yet impossible 

 to say whether at these times there was a real change in the sunspot 

 period, whether some subordinate period is operating in the sun, or 

 whether only local conditions of some kind are the controlling factor. 



The yellow pines of northern Arizona are dry-climate trees. They 

 have a modified winter precipitation of the temperate zone. Spring 

 and autumn have the complete dryness of the " horse latitudes," and 

 the summers have the characteristic subtropical torrential thunder- 



