GROWTH IN TREES. 



33 



although others in more exposed localities had made elongations of 

 2 to 4 cm. of the leafy shoots. A temperature of 8 C. was taken on 

 March 30, and not until April 1 was an upward movement of the pen 

 to be seen, the record for the previous 6 weeks being a level line with 

 but little daily variation. 



Steady and continuous enlargement of the trunk continued until 

 June 20. After a period of quiescence, enlargement again began on 

 July 3, continuing until July 25. A total increase of 4.5 mm. in 

 diameter had taken place (fig. 10). 



After a period of quiescence, with no indication of further seasonal 

 enlargement, five drain tiles, 75 cm. long, were set vertically in the 

 loose sandy soil around the tree within a radius of 2 meters from the 

 trunk, and water was turned into these openings so that 2,000 gallons 

 were taken in without overflow between 5 h 30 ra p. m. of August 1 and 



AUG. 16 1920 



FIG. 11. Dendrographic records of California live oak No. 2 illustrated in fig. 10. A condition 

 of quiescence had been reached when irrigation was begun before 6 p. m. on August 16, with a 

 quick response in increase in diameter which continued through the week and until the middle 

 of the following week, as shown in the record in the middle of the figure. Quiescence with but 

 little daily variation is indicated in the record of the week beginning August 30. Some shrinkage 

 ensued in the week beginning September 6, 1920. Variations are X 15 on a scale with 10 mm. 

 intervals. 



7 h 30 m a. m. the next morning, and 1,000 gallons were added on the 

 second night. The soil previous to irrigation had become so dry that 

 it had a moisture content of less than 6 per cent. The consequences 

 of the irrigation were extremely startling. Within 2 hours an enlarge- 

 ment was recorded by the dendrograph, which continued so that during 

 this week an actual increase of about 0.5 mm. had taken place in the 

 diameter of the trunk, including the bark. The rate soon slackened, 

 however, and no growth was visible on August 27, at which time a 

 total accretion of 1 mm. had been made to the diameter (fig. 11). 



