COLLECTION OF SECTIONS. 



35 



usual way by a straight sloping line reading 1.90 mm. in 1820 and 1.15 

 mm. in 1910. The corrected means smoothed by Hann's formula will 

 be found plotted in figure 24. 



TABLE 3. 



CHRISTIANIA GROUP. 



This group of 5 Pinus silvestris sections was secured from logs at a 

 little sawmill in the outskirts of Christiania. The logs cut in the 

 neighborhood were in a large pile at the mill, and after the snow was 

 brushed from them suitable ones were selected. Usually in such cases 

 the largest and oldest were taken, but in this group the growth was 

 exceptionally complacent. Accordingly, preference was given to those 

 which showed variability in size of rings. 



These sections were measured a' month or two later. Cross-identi- 

 fication proved very unsatisfactory. Large variations were found in 

 the 5 specimens. On this account it was felt that there might be 

 several errors in this group which could perhaps have been removed 

 by a larger number of trees for intercomparison. The centers of the 

 5 were respectively at 1848, 1824, 1797, 1807, and 1790. The average 

 diameter was about 1 foot. On page 1 14 will be found the mean growth 

 of these sections and the plot of the same will be found in figure 8. 

 There seems no special change in growth with age, and the whole series 

 was merely reduced to percentages by dividing each yearly value by 

 1.50 mm. These values, smoothed by Hann's formula, will be found 

 plotted in figure 23. 



CENTRAL SWEDEN GROUP. 



These 12 sections, showing an average diameter of about 11 inches 

 and an average age, of 190 years, were obtained from the sawmill near 

 Gefle, on the coast, 60 miles north of Stockholm. The mill, one of the 

 largest in Sweden, was some 4 miles from the town, on the river coming 



