42 CLIMATIC CYCLES AND TREE-GROWTH. 
increase was interpreted to mean that at that time these hemlocks 
emerged from the shade of surrounding trees. The change was so 
rapid and great that it seemed likely to be due to the cutting down of 
the surrounding forest. In this subgroup, also, the years 1770 and 
1821 were so extremely small that injury on those dates seemed 
likely.’ The other subgroup from east of Windsor extends easily to 
1650, with one extrapolation of 20 years and another of 3. It shows no 
effects in 1770 or 1821, but does show a temporary slight rise in 1807, 
and then a gradual increase to well over 2 mm. by 1870 or 1880, as 
would be expected when light-loving trees gradually push their way 
out into preeminence above their neighbors. A comparison between 
these two curves in their minor details confirms the view that all 11 
may be included in one group. 
The means of the Windsor hemlock sections from 1651 to 1912 are 
given on page 116. In 1651 the figures give an average derived from 
only 6 sections. This increases to 9 sections in 1694, and from 1695 the 
whole 11 sections are used. These numbers have been smoothed and 
plotted,.and their resulting curves will be found in figure 27, oa 
with the sunspot curve. 
OREGON GROUP. 
Following the New England group, a set of Douglas firs was obtained 
from a logging area about 25 miles northwest of Portland, Oregon. 
Several points of interest appear in connection with this group. In the 
first place, the samples were not radial specimens of the wood itself as 
heretofore, but were pieces of blotting-paper of suitable size which had 
been rubbed into the tops of the weathered tree stumps. These were 
made in 1912 by Mr. Robert H. Weinknecht, who writes as follows: 
“The prevailing age on the tract is about 210 years on the stump. The 
trees selected were average with neither suppressed nor abnormally large 
growth. An average typical radius was selected on each stump. Twenty- 
three impressions from this one locality were obtained and sent. ‘Twenty-one 
came from stumps cut in the summer of 1908, one from a stump cut in 1909, 
and one from.a stump cut in 1912. The method of taking the impressions 
was one devised by Mr. Higgs and described by him in the Forest Quarterly 
for March, 1912. It was found that fresh stumps gave very poor results 
and especially poor for the last 50 years. This was attributed to pitch form- 
ing near the outer parts of the stump and to the fact that the weathering of 
the stump had not been sufficient to bring the rings out in relief. Some of 
the impressions were gone over with a pencil to bring out the rings where 
they were faint or broken. This was done carefully and checked by the 
number of rings counted on the stump.” 
During the course of identification and measurement, it was observed 
that only a small proportion of the ring impressions show distinctly 
1 A letter was published in the local newspaper, asking if anyone had any information regard- 
ing forest fires in 1770 or 1821 or of lumbering in that locality in 1807 or 1808, but no reply has 
been received. 
