432 
Journal of Agricultural Research 
Vol. XXXI, No. 5 
to cell action as would defeat the end in view, consequently the sur¬ 
rounding air and the soil in which the roots are growing must be 
relied upon to furnish such determinations. 
Fortunately the trunk of the date palm, with its single enormous 
terminal bud, within which all leaf growth and elongation takes place, 
affords ample space in which to place a thermometer without serious 
disturbance to the functions of the plant. 
For a study of interior temperatures by this method, a Zaheedy 
male seedling, 6 one of the trees upon which leaf growth records have 
been kept at the United States Date Garden at Indio, Calif., was 
first selected. It had a trunk height of 5.5 feet and a diameter (out¬ 
side of the leaf bases) of 18 inches at 2 feet from the ground. At 4 
feet from the ground, or 18 inches below the top of the bud, its diam¬ 
eter was 13 inches. Two %-inch holes were bored to the center of 
the trunk, one 18 inches below the apex of the bud, and one on the 
opposite side of the tree at 30 inches from the ground. A 13-inch 
chemical thermometer was inserted in each hole after being pushed 
through perforated corks to close the holes and yet permitting the 
bulbs to reach the center of the trunk. The bulbs were covered 
with sleeves of thin rubber tubing to prevent too quick a change in 
the readings. A third thermometer was installed in a frame close to 
the trunk of the tree and screened so as to give practically the condi¬ 
tions of a Weather Bureau shelter. A soil thermometer exposed at 
2 feet deep in the same grove, 100 yards distant, furnished the soil 
temperature comparison. Observations were begun at 3 p. m. on 
February 18, 1918, a heavy snowstorm in the mountains surrounding 
the Coachella Valley indicating that a sharp frost might be expected 
on the following morning. Somewhat irregular observations were kept 
upon these thermometers during the next three months, from early 
morning till 9 or 10 p. m., in a few instances until a later hour, and 
one all-night record was made, the readings being taken from a half 
hour to two hours apart, according to the critical period of the record. 
Readings of the lower thermometer in the Zaheedy tree were discon¬ 
tinued for a time after March 15, and a second tree, a Maktoom, 6 was 
used as a check, to ascertain whether the daily curve developed in the 
temperatures of the Zaheedy tree might be considered characteristic 
of the species. 
These observations, continued until the end of May, became too 
voluminous for complete presentation within the^scope of this article. 
Five periods of six to eight consecutive days each have been selected 
as bringing out most effectively the important points disclosed by 
these studies, and their records tabulated and in part presented in 
graphs in their relation to current air and soil temperatures. 
The readings of the thermometers in the Zaheedy tree from Feb¬ 
ruary 18 to 25, inclusive, showing the response to the lowest tempera¬ 
tures encountered, are shown in Table I and the corresponding graphs 
in Figure 5. Table II shows the records of this tree from March 1 
to 6, inclusive, a period when the daily air maxima were 80° F., but 
with the minima of the last two days suddenly lifted from between 
46° and 48° to above 56°. 
• For convenience referred to as the Zaheedy and Maktoom trees. 
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