32 



GROWTH IN TREES. 



interruptions, until about January 18, 1920. The total accretions 

 amounted to about 5 mm. in diameter, of which some was lost by the 

 shrinkage described. 1 



Changes in size consequent upon rains followed until the instrument 

 was replaced on February 9, 1920, by a model using the belts of blocks 

 for a base, but retaining the U-shaped floating frame of bario. New 

 shoots 5 to 8 cm. long and leaves one-third full size were noted on 

 March 15, but no enlargement of the trunk had yet occurred. Actual 

 enlargement did not begin until April 9, one month later than in the 

 previous year. 



The instrument was jammed for 2 weeks, but when set in order 

 showed continued action, justifying an estimate of the accretion not 

 recorded. Growth at a decreasing rate continued until August 1, at 

 which time a total increase of 4.6 mm. had ensued. After this time 

 the record varied but little from a level line and the instrument was 

 dismounted on September 24, 1920, the record being continuous since 

 February 24, 1919, a period of 19 months and including two entire 



seasons. 



JULY II I9EO 



6PM !'- ','. 



6PM 6AM 6PM 6A\i 



6PM 6AM 6PH_ 6AM 6PM. 



CA.M fiPM GAM 



-39- 



MAY 31 1920 



MARCH 15 1920 



FIG. 10. Dendrographic records of California live oak (Quercus agrifolia) No. 2. Beginning 

 growth, denoted by upward course of the tracing, is shown in the week beginning March 15, 1920, 

 and vigorous growth in week beginning May 31. Quiescence with small daily variations are seen 

 in week beginning July 11. Variations are X 15 on a scale of 10 mm. intervals. 



The measurements of a second oak were taken for 1920 by an instru- 

 ment in which the floating frame was make up of three bars of invar 

 and one bar of bario. The bark was intact and turgid, the trunk 

 having a circumference of 54 cm. at the place of measurement, 1.3 

 meters above the ground. The levers were set to amplify 16 times and 

 a thermometer was set in the bark to take temperatures of the north 

 side at about a centimeter below the surface. No growth was to be 

 seen in the tips of the branches of this tree on February 11, 1920, 



1 The above statements are in part corrections of the preliminary report on this tree: The growth 

 of an oak trunk. Carnegie Inst. Wash. Year Book for 1919, see p. 77. 



