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 0.38 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." The 
method of irrigation was calculated to wet the absorbing surfaces of 
theseroots Theactual path to be traversed from the absorbing surfaces 
MARCH 10-17 1919 ™ 
6PM12PMG6AM M. 6pm 12PMGAM. M.6PM.12PM6AM. M. 6PM.12PM.6AM_M. 6PM.I2PM6AM. M. 6PM12PM6AM_M. 6PM 12PM6AM. 
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Fig. 12.—Dendrographic record of growth and variations in Arizona ash (Frazinus arizonica) 
for the week beginning March 10,1919. Temperature of cambium region ranged from 6° to 24° C 
A period of temperaturea 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 
1Cannon, W.%A. Tree distribution in central California. Pop. Sci. Monthly, 85:417:424. 
Nov. 1914. See pp. 420-421 and fig. 3. 
