22 GROWTH IN TREES. 



layer 3 mm. in thickness had taken place during the first half of the 

 season in that year. Of the 31 layers or rings of this tree, one was 

 added by irrigation in 1920, one has the appearance of resulting from 

 autumnal rains in 1918, one very thin one was piobably formed under 

 such circumstances in 1907, and another in 1904. The tree may 

 therefore be considered as being 27 years old at the beginning of the 

 season of 1921. 



During 1920 a second instrument was placed on the trunk, 8 meters 

 above the ground. Tree No. 2 of this species was about 18 meters in 

 height and 40 cm. in diameter near the base, with heavier branches 

 than No. 1, and stood on a sandy slope facing northward. A wide 

 variety of devices was tested on the instruments attached to this tree, 

 so that no continuous record, such as that which has been obtained 

 from No. 1, was obtained. 



Monterey pine No. 6 was the smallest tree of this species to which the 

 dendrograph with floating frame was applied. It was about 10 meters 

 in height, 16 cm. in diameter near the ground, and stood on a north- 

 facing slope in position where the direct sunlight did not strike the 

 ground, which therefore remained at a lower temperature and with a 

 higher moisture content than the other trees. The presence of 20 

 rings or layers indicated an age of 17 years. The layer formed in 1920 

 had a thickness of 3 mm., which was equivalent to that of 1919, and 

 the secondary layers of 1907 and 1904 were plainly apparent. 



No. 7 was about 14 meters in height and 35 cm. in diameter near the 

 base. Observations on this tree were confined to dendrographic 

 measurements of the woody cylinder from bearings made at the bottom 

 of borings extending through the wood of the previous year. Tem- 

 peratures of the outer layer of the trunk and of the heart were also 

 taken by mercurial thermometers. This tree stood on a north-facing 

 slope of a "fog channel" near No. 6, which was exposed to similar 

 conditions. 



The most obvious points of interest in the growth program of each 

 year are those which concern the dates of awakening and cessation of 

 growth of terminals and of the trunk. 



Elongation of terminals of No. 1 began early in February 1919, but 

 no enlargment of the trunk was measurable until March 30. A 

 period of low relative humidity and high temperature resulted in no 

 increase in diameter of the trunk between May 29 and June 6, after 

 which enlargement took place at a low rate for a few days, alternating 

 with periods in which only reversible variations were discernible. 

 This later phase of growth might be identifiable with an after develop- 

 ment of phloem, such as has been described by Brown 1 in Pinus 

 strobus. The total net accretion on the diameter measured by the den- 



1 Brown, H. P. Growth studies of forest trees. Bot. Gaz., 59:237. 1915. 



