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 0.2mm. 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 
mm. 
No./ \ 
+0 
> 
a owt ap 
A LY h2 
No.2 Wd a Ve" aALaAario 
=| | Sy Ais = a8 
No.3 2 Ro V Ms \ sur ewe 
1710 1750 Years 1600 Lh 
No./ : Ma af A 7 
P42 
Nat fone at p~AA L\ 10 
sn tas I>. me “ Nu V 08 
Sa US Es Ss SO Oe a 
N0.3¢°~4-% \~ 
185 
1810 B50 ania 1900 
Fic. 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 
