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. 



o 



c 



30 



25 

 20 



1870 



1880 



Year 



1890 



1900 



1910 



= 15 



10 







V 



V 



: 



3.0 



2.0 



1.0 



o 



0.0 



FIG. 7. Annual rainfall and growth of trees (Group V) at Prescott. Dotted line: rainfall. 



Solid line: growth. 



I 



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, Pmws si7yesm, and averaged about a foot 

 in diameter. The growth was very rapid and the wood was full of 



