34 



GROWTH IN TREES. 



The experiment was repeated by giving the soil around the tree 

 2,000 gallons at 9 p. m. on September 15. Again a swelling 

 was noticeable within 4 hours after the water was laid on, and not 

 more than 800 gallons had been given the soil. Enlargement con- 

 tinued for 3 days, with a total addition of 0.3 mm. to the thickness of 

 the trunk. In the ensuing quiescent period no shrinkage occurred, 

 and no swelling resulted from the rains of October 6 and 8. The 

 instrument was now dismounted. 



The readiness of reaction of the live oak to increased soil-water 

 supply and the shorter period of enlargement and small relative total 

 are in contrast with the reactions of the pine growing in similar soil 

 a few meters distant. The root system has been described by Cannon 

 as including a well-developed superficial portion consisting of numerous 

 short, slender roots which lie within a meter of the surface. 1 The 

 method of irrigation was calculated to wet the absorbing surfaces of 

 these roots The actual path to be traversed from the absorbing surfaces 



MARCH ICH7 1919*-.. 



Fio. 12. Dendrographio record of growth and variations in Arizona ash (Fraxinufaritonica) 

 for the week beginning March 10, 1919. Temperature of cambium region ranged from 6 to 24 C 

 A period of temperatures from 6 to 9 C. on the 15th and 16th was characterized by little, 

 shrinkage. Variations are X 10 on a scale of 10 mm. intervals. 



to the part of the trunk in which swelling was measured was not less 

 than 2 meters, and this was traversed by the water supply in such 

 quantity as to be measurable in less than 4 hours. 



GROWTH OF THE ARIZONA ASH. 



The Arizona ash (Fraxinus arizonica), a rapidly growing species 

 which forms a trunk 25 to 50 cm. in diameter, occurs along streamways 

 in Arizona and New Mexico. It is planted around dwellings and the 

 size attained appears to bear a direct relation to the available water 

 supply. 



A dendrograph, with a floating frame of bario having two bearing 

 points opposite the lever, was attached to a tree near the residence 

 of Dr. H. W. Fenner, in Tucson, Arizona, on March 8, 1919, and a 

 thermometer was thrust under the bark. The instrument was set 

 to amplify the variations ten times in the record. The trunk was 

 almost exactly 1 meter in circumference and was compressed in one 

 diameter. Irrigation practice had begun for the season and the 



1 Cannon, W.? A. Tree distribution in central California. Pop. Sci. Monthly, 85:417:424. 

 Nov. 1914. See pp. 420-421 and fig. 3. 



