26 



GROWTH IN TREES. 



reversible variations with some slight increases on both places on the 

 trunk following a rain on October 14. Again some increases occurred, 

 beginning on November 16. Similar period of increase occurred in 

 December. No actual seasonal or winter shrinkages of the stem at 

 either point could be detected. 



Very interesting occurrences of this sort, however, were observed in 

 connection with rains. On April 15-16, December 21-23, 30-31, 

 a continuous enlargement of the trunk took place which would be 

 wholly or almost wholly lost on the sunny day following. 



AUG. 16 1920 



FIG. 7. Dendrographic record of the variations of lower and upper parts of trunk of Monterey 

 pine No. 1 at end of period affected by irrigation. 



The present record is closed on January 27, 1921, at which time the 

 staminate flowers were nearly mature and the terminal buds were 

 beginning to swell, and some actual enlargement of the trunk had 

 begun and was still in progress on January 31. 



During 1920 the basal part of the trunk had shown a total enlarge- 

 ment of nearly 9 mm. in diameter, and the section 8 meters from the 

 ground about 6 mm. The accretion of 1920 appeared in borings at the 

 base of the tree as two layers in two cores 5 and 4 mm. in thickness, 

 when measured at the end of January 1921. The outer layer may be 

 taken as representing accretion following irrigation, which, it may be 

 suggested, may have been largely in the phloem. The borings at the 

 higher point snowed two layers, 4 and 2 mm. in thickness. 



Awakening of buds took place several weeks before enlargement of 

 the trunk began in 1919 and 1920, but in 1921 growth of both kinds 

 was apparent the last week in January, nearly two months earlier than 

 the observed dates of enlargement of trunks in previous years. 



The variations of a younger tree were sought by the attachment of 

 an instrument to Monterey pine No. 6 on February 12, 1920. This 

 tree may be identified as beginning in 1904, as it made a second layer 

 of wood in its first year and shows the extra formations in 1907 and 

 1918. The floating frame of the instrument was of invar, the levers 

 being set at first to amplify 5 and later to 15 times. The trunk had a 

 diameter of 18 cm. and the first discernible enlargement was on 



