COLLECTION OF SECTIONS. 



43 



the ending of each year's growth, which is usually the best measuring- 

 point. In good reproductions the measures are satisfactory, different 

 observers agreeing within 0.1 to 0.2 mm. In others, however, there is 

 much chance for judgment in selecting the measuring-point, and 

 observers differ 0.3 to 0.5 mm. Nevertheless it is easy to judge of the 

 relative sizes of rings and the only injurious effect is to reduce variations. 

 The cross-identification was very satisfactory, with practically no 

 doubtful cases and only a few which required careful study. It is not 

 likely that there is a single error in identity throughout the 17 sections 

 in this group. Two other trees, one cut in 1909 and the other of 



No.l 



No.Z 



No. 3 



17/0 



No.l 



No. 2 

 No.3 



s 





- 



' 



HA 



f\/\ 



V 



1810 



1850 



Z 



I 





 I.Z 

 1.0 

 0.8 



Years 



1300 



FIG. 11. Oregon group. Curve No. 1, actual tree-growth; No. 2, tree-growth 

 departures, smoothed; No. 3, sunspot numbers displaced 2 years to left. 



unknown date, but probably cut in 1902, were not included. They 

 showed special characteristics, such as an evident injury in 1861-62, 

 affecting the 1862 ring and several others following it. They show 

 also small growth in 1886, and even in 1887 and 1888 following the 

 minimum growth of 1884 and 1885 prominent in the large group. The 

 tree (cut probably in 1902) shows a minute growth in the years 1779 

 to 1783 inclusive, evidently the result of injury. These two sections 

 are full of character and may prove valuable. 



Five other rubbings similar to the group of 17 were discarded 

 because defective in some parts. The attempt to trace the lost lines 

 with a pencil-mark gave no help. One of the 17 was defective since 



