GROWTH IN TREES. 



27 



March 16, after which acceleration carried growth to a maximum rate 

 in the last 10 days of April. The rate now slackened and growth 

 ceased about June 1, with a total increase of 4.5 mm. in diameter. 



A rain on June 14 was followed by some growth in the following 

 week, after a period of reversible alterations ensued. Not until late 

 in July did a slight enlargement recur and a similar impulse was re- 

 corded at the end of August (fig. 8). No further increase could be 

 detected, but a shrinkage began on October 11 which continued until 



SEPT. 20 I9ZO 



6PM 6AM 



6P.M. 



6AM 6P.II 



FIG. 8. Dendrographic records of Monterey pine No. 6, with no growth in week of March 1, 

 1920, beginning growth in week of March 22-29, vigorous enlargement in week April 12-19 daily 

 equalizing variations of wide amplitude in week of June 28-July 5, and reduced variations late in 

 September. Variations X 5 on scale of 10 mm. intervals. 



the instrument was dismounted a week later. A total increase of 

 5 mm. had been recorded. It is to be noted that the terminals and 

 tips of the branches had made a growth of several centimeters when 

 the observations were begun, and that such elongation must have 

 started about two months prior to the increase in the trunk. 



Measurement of another pine (Pinus chihuahuana) , on the slopes 

 of the Santa Catalina mountains, an isolated range near the Desert 

 Laboratory, gave a set of results under conditions different from those 

 afforded by the indeterminate seasons of the coastal climate. A tree 

 40 cm. in diameter, in the lower edge of the pine belt at about 2,000 

 meters, was selected for observation. This location is characterized 

 by a coarse granitic soil, winter and mid-summer rainfall; minimum 

 air temperatures of 8 C. and summer maxima of 40 C. are of record. 



