GROWTH IN TREES. 31 



GROWTH OF THE CALIFORNIA LIVE OAK. 



The California live oak (Quercus agrifolia'), which is* one of the 

 commonest of the oaks of the Pacific slope and in the region of the 

 Coastal Laboratory, is a small tree with trunks 25 to 50 cm. in diameter. 

 The leaves of one season remain on the tree until those of the next 

 season are unfolding, which in this region begins early in February. 

 The first indication of awakening activity is the elongation of the 

 leafy branches which may occur in some individuals 2 or 3 weeks earlier 

 than in others a short distance away. As will be seen from the records 

 discussed below, enlargement of the trunk began in March, somewhat 

 earlier than in the Monterey pine in the same locality. 



Measurement of this species includes one feature widely different 

 from the pines, in that the bark remains alive and turgid until it 

 reaches a thickness as much as 5 cm., and it is upon the surface of this 

 structure that dendrographic bearings must be taken. The bark 

 finally becomes deeply and irregularly furrowed, so that any single 

 line around a tree may cross not more than three or four of such 

 rifts, which appear to go nearly to the wood, a condition which was 

 found in the first tree measured. 



A dendrograph with a floating frame of bario in the shape of a large 

 U was mounted on a rectangular frame support and put in place on 

 No. 1 of this tree on February 17, 1919. On March 1 a slight increase 

 was recorded, but not until March 11 did positive growth begin and 

 this continued until the end of May. Temperatures (1 cm. interior to 

 the surface of the bark) of 7 to 9 C. were recorded during February 

 and March, rising to 14 C. during the growing period. Later in the 

 summer records of 18 C. were taken. 



Continuous records were kept and on February 10, 1920, the instru- 

 ment was changed to one using a belt of blocks as a support for the 

 floating frame of bario. No growth of the tips of the branches had 

 yet taken place and temperatures as low as 6 C. were noted on several 

 mornings. One record of 9 C. was taken as late as March 30 in the 

 growing season. 



The daily variations in this type of tree are very slight, so that the 

 record did not vary widely from a level line until March 10, when it 

 began to take an upward course which was not slackened until after 

 May 5. Growth was again actively in progress by the 18th, to slow 

 down again by the 28th, a shrinkage of marked character taking place 

 during the following week, followed by quiescence. 



Growth was resumed on June 18, but soon ceased. Another impulse 

 between June 22-28, another September 25-28, were observable. A 

 decided shrinkage began on September 30, which continued for 7 days. 

 An increase took place during the last 10 days in October, and a very 

 marked shrinkage began December 1, which continued, with some 



