GROWTH IN TREES. 23 
drograph was 9 mm. and the thickness of this layer (laid down in 1919) 
taken from a boring on another diameter, in January 1921, was about 
8 mm. 
Heavy rains beginning on November 26, 1919, were followed by an 
increase beginning on November 29, which continued until De- 
cember 14. A similar slight increase following rain took place early 
in January and late in January. 
The instrument was reset on February 9, 1920, and a second one 
reached by a scaffolding attached at a point 8 meters above it, both 
making a record in which the variations in diameter were amplified 
8 times (see fig. 4). The circumference of the trunk at the upper in- 
strument was 100 cm. as compared with 130 cm. at the lower one. 
The levers of both instruments were set to give an amplification of 
8 times, so that it was possible to make direct comparisons of the ac- 
tion of the trunk in the two places. The bark in both cases was thinned 
so that the contacts were made on layers of cork not more than a 
millimeter in thickness. The bark at the base of the tree was heavy 
and was coming away in flakes, while that at the upper instrument 
had begun to show only shallow rifts and was not more than 3 or 
4 mm. thick at any place. Thermometers thrust under the bark on 
the north side of the trunk showed temperatures as low as 6° C. on the 
date mentioned and as low as 8° C. on March 30. 
Some enlargement of the same type followed rain March 18 to 22, 
but this was followed by a period of reversing variations, and not until 
April 7 did a continuing enlargement begin which showed an initial 
rate slightly greater than that at the uppermost instrument, which 
began on the same day (fig. 5). 
As this manuscript is being completed, the records for the early 
part of 1921 are available. They show that the tips of the branches 
on young and old trees began to grow about mid-January, and that the 
enlargement of the upper part of the trunk of this tree showed en- 
largement on the 27th of January, 2 days earlier than any increase 
of the lower part of the trunk. Action in the two places was syn- 
chronous in 1920, but did not begin until 2 months later than the 
awakening of the tips of the branches. No attempt has yet been 
made to correlate these facts with the activities of the roots, but the 
observations of W. B. McDougall are to the effect that growth of the 
roots begins quite early in the season and that it depends largely upon 
moisture and temperature." 
As in the previous year, a period of reversible variations began late 
in May 1920, which continued until July 2, at which time the soil 
moisture content had come down to 5 to 7 per cent. The total accre- 
tion at the base of the tree was slightly less than 3 mm., slightly 
1McDougall, W.B. The growth of forest tree roots. Amer. Jour. Bot., 3:385-392. 1916. 
