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 grow r ing 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 KH7 



FIQ. 12. Dendrographic record of growth and variations in Arizona ash (Fraxinut ortzontco) 

 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 k !0 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 tunes 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 



Cannon, W. A. Tree distribution in central California. Pop. Sci. Monthly, 86:417:424. 

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



