YELLOW PINES AND SEQUOIAS OF THE SOUTHWEST. 119 



size for many years in succession — or gross in character, which means 

 extraordinarily large rings here and there and the whole grouping 

 apparently subject to slow surges in size as one glances across the 

 sequence from center to bark. Gross rings in one tree have about an 

 equal chance of appearing or not appearing in any other tree near by. 

 Since gross and complacent rings have little individuality, it is not 

 always easy to identify their dates, especially if the outer layers of 

 wood have been cut away as was usually done in felling the sequoias. 

 On the other hand, the slow-growing, low-moisture trees are full of 

 snappy irregularities which may be found in tree after tree, thus 

 rendering accurate dating a remarkably easy process. It is also 

 immediately evident that these latter sensitive trees give short-period 

 variations far more accurately and effectively than the complacent 

 trees. 



A study of cycles of growth in the last five centuries of these 

 twenty-one trees shows that often basin and upland trees vary to- 

 gether, and that in comparison with the others the well-watered trees 

 show no lag of more than three years. Certainty in regard to no lag 

 at all has not yet been reached. 



Out of these latter tests has come the most interesting fact of all 

 to students of cycles. The yellow pines of northern Arizona, much 

 more sensitive than the upland sequoias, show the history of the 

 eleven-year sunspot cycle in a prominent manner, even though other 

 cycles are present. The fairly sensitive upland sequoias show the 

 sunspot cycle, but other cycles are more prominent, and the eleven- 

 year period has to be traced in multiples or harmonics to overcome 

 the various interferences. But the complacent rapid-growing se- 

 quoias show the sunspot cycle only here and there, and so far no 

 certain way has been found of using them in studying the history of 

 that cycle. 



This brings us to the consideration of the cycles in tree growth 

 as climatic products. The ring itself is a result of the seasons. 

 Variations in the rings in dry climates are found to match the rain- 

 fall. But the rings display marked cycles, and if these also can be 

 interpreted as climatic, they are likely to prove of great assistance in 

 studying climatic variations, because they stretch over great historic 



