sept. i, 1925 Inhibitive Effect of Sunlight on Growth of Date Palm 
459 
ascending from left to right show night growth beginning at 6.12 
p. m., 7 p. m., and 7.15 p. m. on April 10, 11, and 12, respectively, 
and ending 6 a. m., 6.10 a. m., and 6.15 a. m. 
Table I .—Daily growth of date palm before and after midnight, with time of 
beginning and ending from April 25 to May 20 
Days 
Apr. 25 to 26- 
Apr. 26 to 27- 
Apr. 27 to 28. 
Apr. 28 to 29. 
Apr. 29 to 30. 
Apr. 30 to May 1 
May 1 to 2. 
May 2 to 3_ 
May 3 to 4. 
May 4 to 5.. 
May 5 to 6.. 
May 6 to 7.. 
May 7 to 8_ 
May 8 to 9_.. 
May 9 to 10- 
May 10 to 11- 
May 11 to 12_ 
May 12 to 13_ 
May 13 to 14_ 
May 14 to 15- 
May 15 to 16_ 
May 16 to 17- 
May 17 to 18_ 
May 18 to 19- 
May 19 to 20_ 
May 20 to 21_ 
Hour 
growth 
was re¬ 
sumed 
Min¬ 
utes 
before 
sunset 
Hour 
growth 
ceased 
Min¬ 
utes 
after 
sunrise 
Growth 
before 
mid¬ 
night 
Growth 
after 
mid¬ 
night 
Total 
growth 
Excess 
of 
growth 
before 
mid¬ 
night 
Excess 
of 
growth 
after 
mid¬ 
night 
p. m. 
a. m. 
Mm. 
Mm. 
Mm. 
Mm. 
Mm. 
5.50 
6.12 
8.0 
9.0 
17.0 
1.0 
5.57 
6.30 
10.0 
8.5 
las 
1.5 
5.40 
7.30 
80 
9.5 
10.5 
20.0 
1.6 
6.50 
15 
7.05 
52 
ao 
11.0 
19.0 
3.0 
7.12 
6.42 
29 
7.5 
9.5 
17.0 
2.0 
5.20 
108 
6.33 
15 
ao 
10.5 
ia5 
1.5 
7.05 
8.10 
120 
8.0 
10.0 
lao 
2.0 
6.15 
9.50 
189 
9.0 
13.0 
22.0 
4.0 
5.55 
85 
8.35 
223 
10.5 
12.5 
23.0 
2.0 
6.12 
69 
6.55 
50 
12.0 
12.0 
24.0 
6.6 
0.0 
7.05 
9.00 
170 
8.5 
11.0 
19.5 
2.5 
6.25 
7.30 
80 
10.0 
10.5 
20.5 
0.5 
4.32 
161 
8.35 
145 
12.5 
10.0 
22.5 
2.5 
4.52 
148 
6.45 
33 
11.0 
8.5 
19.5 
2.5 
5.00 
148 
10.00 
220 
11.5 
9.5 
21.0 
2.0 
6.10 
70 
5.47 
21 
ao 
6.5 
14.5 
1.5 
6.55 
32 
6.15 
9.0 
9.5 
18.5 
0.5 
7.16 
10 
6.15 
9.5 
10.5 
20.0 
1.0 
6.50 
30 
7.50 
110 
8.5 
12.5 
21.0 
4.0 
7.00 
20 
6.12 
8 
10.0 
13.0 
23.0 
3.0 
5.22 
125 
9.00 
180 
12.0 
10.0 
22.0 
2.0 
7.10 
20 
6.45 
36 
10.0 
10.0 
20.0 
0.0 
0.0 
6.43 
51 
8.03 
60 
10.0 
10.0 
20.0 
0.0 
0.0 
6.23 
75 
8.05 
102 
9.0 
11.0 
20.0 
1.0 
6.15 
75 
7.52 
110 
12.0 
9.5 
21.5 
2.5 
6.12 
78 
8.28 
148 
10.0 
12.0 
22.0 
2.0 
Figure 2 shows the daily growth for nine successive days (May 10 
to 19) plotted to a uniform scale; a single line for each night’s growth 
ascending from left to right between the horizontal lines of no growth 
during sunlight. The vertical lines show the hours of growing time 
before and alter midnight, with the lines of heavy dashes indicating 
approximately the time of sunset and sunrise. 
In a general way both Figures 1 and 2 and Table I show that the 
growth activity began at a variable time before sunset, progressed 
rather uniformly through the night and to aperiod of from a few 
minutes to two or three hours after sunrise. The excess of growth in 
the periods before and after midnight appears to depend on the pro¬ 
longation of the growth period by the light being obscured by clouds 
and dust, so that normal growth may be regarded as nearly uniform 
throughout the hours of darkness, it should be noted also that the 
growth rate in obscured sunlight (for example, the evening of May 15 
and the morning of the 16th) is invariably slower than that during 
full darkness. 
Correlated observations on the weather conditions showed that 
when the air was clearest the beginning of growth was retarded the 
nearest to sunset, and growth ceased soonest after sunrise. With 
clouds over the mountain top to the west, obscuring the sunset, or 
with the air heavy with fine sand driven by winds from the same 
direction growth began at an earlier hour. After all-night winds 
which filled the air with dust, or with vapor present in the morning 
