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 he 
