30 GROWTH IN TREES. 



variations. The effects of humidity and temperature will be presented 

 in a later section. A core, taken from this tree by Dr. A. E. Douglass, 

 showed 74 layers or rings which varied from 1 to 5 mm. in thickness, 

 that for 1918 and for 1919 being about the same thickness as the 

 measurement for 1920 just given. 



MEASUREMENTS OF A SPRUCE AND A FIR. 



The Douglas fir (Pseudotsuga taxifolid), at the Alpine Labora- 

 tory on the slopes of Pikes Peak to which the dendrograph was 

 attached, was nearly 36 cm. in diameter and the instrument had 

 an amplification of nearly 16 times. The buds were developing 

 rapidly when observations were begun on June 17, at which time in- 

 crease of the diameter of the trunk was visible in the daily variations. 

 Growth was already in progress. The increase continued at a low 

 rate until July 21, at which time a total gain of 2 mm. in diameter 

 had been made. After some days of equalizing variations, with 

 temporary swellings consequent upon rains, an increase began August 

 11, which continued until the 22d, making the total accretion for the 

 season 2.6 mm. The shrinkage which ensued during the first half of 

 September reduced this total to 2 mm. 



The only continuous record of the growth of this tree which had been 

 made previously is that by Mr. A. Mallock, who measured variations 

 in the girth of a tree which had a circumference of 33^ inches, by 

 means of an invar tape connected with glass prisms arranged to observe 

 movements of interference bands. These observations were made 

 July 5 to July 16, 1917, in England. It is not known whether any 

 growth had taken place earlier in the season, but a shrinkage was in 

 progress during the first 3 days of the observations, after which en- 

 largement began, and continued at a varying rate during the next 8 

 days. Slackening in the rate of growth occurred during the midday 

 period, and the increase was most rapid at night and following rains. 1 



The actual beginning of growth of the trunk was not observed, but 

 probably not much had taken place before the record began, as the 

 buds were just opening. The record of this fir is to be compared with 

 that of a blue spruce (Picea pungens), which was measured by an 

 instrument in the hands of Mr. C. F. Korstian. This tree is on the 

 Cottonwood nursery grounds, 25 miles southeast of Salt Lake City, at 

 an elevation of about 2,250 meters. This tree was 38 cm. in diameter 

 and enlargement was in progress and the buds were opening on June 7. 

 The course of growth was similar to that of the Douglas fir, and as it is 

 being described in an article by Mr. Korstian, in the Botanical 

 Gazette for June 1921, it will not be repeated here. 



1 Mallock, A. Growth of trees, with a note on interference bands formed by rays at small 

 angles. Proc. Roy. Soc., 96 B (see especially p. 193), 1919. 



