COLLECTION OF SECTIONS. * 29 
trees, shows so much greater agreement than the others that it has been 
used alone in drawing final conclusions. Its site was a small, poorly 
drained level space near the bottom of the valley. 
In this group there was no necessity of duplicating the Flagstaff 
records, and therefore small V-shaped cuttings were made at the edges 
of the stumps, only triangular pieces of wood giving the outer half cen- 
tury of ring-growth being brought away. These were the samples on 
which the value of the cross-identification was discovered, as already 
described. Identical series of rings were observed in nearly every tree 
of the group. 
Year 
1870 1880 1890 1900 1910 
30 i 3.0 
2 25 A x * na } A g 
3 ol At iA AL HAS i : ‘loo B 
suf Ny AL a eA 
3 10 i M \ AS Wl Ay ts 1.0 g 
5 LULA 
; V 
0 0.0 
Fie. 7. —Annual rainfall and hated of trees (Group V) at Prescott. Dotted line: rainfall. 
Solid line: growth. 
Out of 67 sections averaging 50 rings each, only 6 gave any identifica- 
tion trouble. In 2 of these, 2 rings were lacking, but when allowance 
was made for this defect the identification was satisfactory. Another 
section had 2 extra rings, and another had 2 extra and 3 lacking. The 
other 2 sections proved especially puzzling and were finally omitted 
from the means. Of these 6 troublesome sections, the first 5 were very 
slow growers. Hence it would seem advisable not to use extremely 
slow-growing trees any more than is necessary. It may be urged that 
trees do not grow continuously at the slow or fast rate and that we can 
not tell how much of the change is due to rainfall. On the whole, how- 
ever, it seems advisable to exclude trees or parts of trees whose identi- 
fication is extremely difficult. The inner rings if well identified may be 
extremely useful in carrying back early records, as the slow-growing 
trees are likely to be among the oldest. 
The averages of 4 subgroups and the means of all the Prescott trees 
will be found plotted in figure 6. The curve of the fifth subgroup is 
given in figure 7, where it may be compared with the rainfall of Prescott. 
SOUTH OF ENGLAND GROUP. 
This group of 11 sections was obtained in January 1913 at Fleet, 
near Aldershot, some 30 miles west-southwest of London. The trees 
were the common pine, Pinus silvestris, and averaged about a foot 
in diameter. The growth was very rapid and the wood was full of 
