GROWTH IN TREES. 



35 



ground was already saturated about the tree. The flower buds were 

 beginning to move, but were not so far advanced as some that were 

 seen on unirrigated land in the vicinity. The conditions were, in fact, 

 as if the plant were growing along a water-course in its natural 

 habitat (fig. 12). 



Enlargement began on March 10 and continued at such rate that 

 an enlargement of 4 mm. had taken place by April 7, a period of 

 28 days (fig. 13). A period of depression and shrinkage, for 5 days 

 during a cold storm, was followed by a resumption of growth which 

 continued until August 25. Another period of depression ensued, 

 but 6 days afterwards enlargement was again noticeable which lasted 

 for a week, and other such impulses were displayed in September and 



Fio. 13. Dendrographic record of growth for the week beginning May 5, 1919, at a time when 

 the daily variations were at a maximum. Relative humidity was low and transpiration was high 

 during the midday period, at which time great shrinkage look place. Variations X 10 on a scale 

 of 10 mm. 



FIQ. 14. Variations in Arizona ash during a final period of slow enlargement near the close of 

 the season, October 13 to 20, 1919. Variations X 10 on a scale of 10 mm. intervals. 



October (fig. 14) ; after this equalizing variations of diminishing ampli- 

 tude only were seen until leaf -fall occurred about November 17 to 24, 

 after which the record was nearly a level line until January. 



The total increase in the diameter of the tree during the season 

 amounted to about 26 mm., and a core taken from the trunk below the 

 bearings on April 20, 1921, showed a layer of 12 mm. 



This instrument was replaced by a new setting on January 10, 1920, 

 with an amplification of 5 times, and the record was a continued level 

 line until April, when some equalizing daily variations began which 

 were the only changes until June 10. An enlargement now began 

 which continued until about July 20 with a depression of the rate in 

 the last week in June, which may be coupled with the high temperatures 

 and insufficient water supply of that period. Then followed only 



