96 CLIMATIC CYCLES AND TREE-GROWTH 



at the time " partial ring study." As far as the matter was carried, 

 the autumn growth was found to be much more closely proportional 

 to the spring growth and to the winter rains than to the summer 

 rains. The matter is one of some complexity, because records of the 

 rains themselves are extremely incomplete, owing to their local and 

 torrential character and heavy run-off. As a result, the tree-records 

 of such rains are local and seem of much less value at the present 

 stage of their interpretation. 



Doubles and cycles — In the early Flagstaff work there were two 

 500-year trees which showed a remarkable half sunspot cycle for 

 nearly 200 years, beginning soon after 1400. One of these was espe- 

 cially perfect in this cycle, showing it with most remarkable regularity 

 (see fig. 17 and Volume I, fig. 32). This tree also was full of double 

 rings. It has suggested the general question as to the character of the 

 record of trees which show many double rings. Is such a record 

 different from those in other trees? So far the answer is thought to be 

 negative, but there is further work to be done on this point. 



Doubles and high altitude — As one studies the upper levels of the 

 yellow pine, above 7,000 feet elevation near Flagstaff, the double or 

 extra ring becomes less and less common. So far as tests go, it does 

 not appear at all in the highest trees. In these higher trees the rings 

 are more complacent, there is apt to be less pitch, and so less red color, 

 in the autumn part; yet this autumn part shows a large proportionate 

 size. Here probably the summer rains play less part in the tree's life, 

 for they are too local and the run-off is too big. But the winter snows 

 especially are too heavy, the ground stays moister, and falling tem- 

 perature is more often the agent which stops the yearly growth. 



Other trees — As stated above, the yellow pine in California shows 

 very rare doubling. Douglas firs and sequoias practically never have 

 it, but piny on and juniper at the lower levels in Arizona are badly 

 subject to it. 



Large single rings — If rains in Arizona are abundant and well 

 distributed, growth extends beyond the summer period. A good 

 distribution here does not mean that they assume at all an even dis- 

 tribution, for in many years evident division into wet and dry 

 seasons has never failed. In a long drought the summer and winter 

 rains decrease and the spring and autumn rains disappear, sometimes 

 entirely. In wet periods, summer and winter rains are heavy, and 

 spring and autumn rains come every few weeks. In this latter event 

 the trees carry their growing-season into autumn. Thus, without 

 putting on any preliminary red ring, they show a wide growth of 

 white tissue, ended in autumn by a dense, narrow red ring. 



Rings in buried trees — In the vicinity of Flagstaff a considerable 

 number of buried trees have been washed out at depths from 18 



