II. PRELIMINARY STUDIES ON THE YELLOW PINE. 

 YEARLY IDENTITY AND THE DATING OF RINGS. 



In comparing the growth of trees with rainfall and other data, it is 

 essential that the date of formation of any individual ring shall be cer- 

 tain. This depends directly on the yearly identity of the rings or the 

 certainty with which one ring and only one is formed each year. The 

 fundamental starting-point in all identification is the ring partially 

 formed at the time of cutting the tree. This is usually found with ease 

 and has led to no uncertainty in the pine. In the sequoia this partial 

 ring is exceedingly soft and had been rubbed off in nearly all trees 

 examined. It was found unmistakably in a tree cut on the date of visit. 



Superficial counting of rings is subject to errors due to omission and 

 doubling of rings. In the first investigation of trees at Flagstaff it was 

 supposed that the results were subject to an error of 2 per cent, most 

 of which arose from double rings near the center of the tree. But the 

 discovery and application of the method of cross-identification revolu- 

 tionized the process of ring identification, and it was proved that the 

 error of unchecked counting in the Arizona pines was 4 per cent and 

 lay almost entirely in the recent years. It was due to the omission of 

 rings or the fusion of several together. 



Apart from cross-identification, confidence in the yearly identity 

 of rings comes from the following sources: 



(1) Belief that the well-marked seasons of the year cause absolute 

 stoppage of growth in winter. The January mean temperature at 

 Flagstaff is 29 F. and that of July is 65 F. 



(2) The known time of cutting of nearly 100 different trees dis- 

 tributed through perhaps a dozen different years successfully and 

 accurately checks cross-identification in the later years of the tree. 



(3) The various identifications adopted for recent years check 

 exactly with the neighboring rainfall records in Prescott and other 

 places where such comparison can be made. This will have further 

 illustration in connection with the chapter on rainfall and tree-growth. 



(4) A check on the accuracy of the accepted identification of the 

 Flagstaff trees was made by noting every statement of weather, freshets, 

 or crop-failures mentioned by the historian Bancroft in his accounts 

 of the settlements of Arizona and New Mexico. There were 14 cases 

 in which the noted feature of the year agrees with the tree-record to 

 one doubtful disagreement. The most striking correspondences occur 

 with reference to the flood on the Rio Grande in 1680, the famines 

 between 1680 and 1690, and the droughts in Arizona in 1748, 1780, 

 and 1820-23. 



The effect of the undetected omission or the doubling of the rings 

 in individual trees is to lessen the intensity of the variations in the 

 curve of growth obtained by the averaging of many trees. T 1 



