Sept. 1, 1925 
Minimum Temperature for Growth of Date Palm 
403 
the complete cessation of growth in the date palms under observa¬ 
tion, which afford the closest approximation to the specific zero point 
that has yet been secured under field conditions. 
After the mild weather and free growth of November and early 
December, the temperatures from December 7 were decidedly 
lower (fig. 1, Table I). For 12 days, from December 8 to 19, in¬ 
clusive, while the mean maximum was still 68.8° F., there were 11 
minimum records below 32° and the mean of the minima was 27.8°. 
There were 4 mornings with a minimum of 25°, and the lowest point 
reached was 21° on December 10. The retarding influence of suc¬ 
cessive minima almost continuously below the freezing point was 
very evident in the early part of this period. 
Table I .—Temperature and daily growth records of varieties of date palm, Indio, 
Calif., December, 1916 
[Critical low temperatures and approximation to zero of growth are indicated by boldface type] 
Temperature 
Mean daily growth of varieties 
Date 
Maxi¬ 
mum 
Mini¬ 
mum 
Mean 
Asherasi 
Deglet 
Noor 
Thoory 
Zaheedy 
Dec. 1 __ _ 
O jp 
73 
° F. 
44 
° F. 
58.5 
Mm. 
12.7 
Mm. 
11.70 
Mm. 
9.20 
Mm. 
5.20 
2. . . 
72 
41 
56.5 
11.9 
13.50 
9.70 
4.60 
3._. 
76 
55 
65.5 
7.6 
11.70 
9.70 
4.50 
4. _ 
75 
52 
63.5 
13.0 
14.00 
10.00 
6.70 
5. ... 
79 
47 
63.0 
12.5 
14.50 
11.10 
8.00 
6 ... 
73 
48 
60.5 
12.0 
15.30 
10.90 
8.00 
7 __ _ ___ 
61 
35 
48.0 
7.0 
11.40 
10.40 
7.40 
8 .. 
62 
26 
44.0 
10.7 
12.30 
10.50 
5.70 
9 _ 
65 
25 
45.0 
7.0 
6.90 
4.80 
2.70 
10 .. 
68 
21 
44.5 
3.6 
2.60 
4.10 
1.50 
11_ 
65 
25 
45.0 
2.7 
1.90 
2.40 
.50 
12 .. 
67 
25 
46.0 
5.4 
1.60 
2.50 
1.00 
13 __ _ 
74 
30 
52.0 
5.0 
.30 
2.10 
.26 
14 . . 
79 
35 
57.0 
3.2 
1.20 
1.60 
.75 
15_ _ _ 
73 
28 
50.5 
3.4 
2.20 
1.80 
.90 
16 . . 
73 
25 
49.0 
3.4 
2.10 
1 . 10 
1.30 
17 ...... 
69 
28 
48.5 
2.4 
2.80 
2.40 
1.06 
18 .. 
72 
31 
51.5 
5.4 
1.60 
1.60 
1.06 
19 ____ 
67 
27 
47.0 
5.6 
3.00 
1.70 
1.00 
20 ... 
65 
40 
52.5 
3.2 
.65 
1 . 16 
.80 
21 ___ 
71 
34 
52.5 
5.9 
1.90 
1.75 
.40 
22 .. 
68 
37 
52.5 
4.5 
2.60 
1.80 
1 . 10 
23 .... 
65 
36 
50.5 
3.6 
2.10 
1 . 10 
1.20 
24 .. 
68 
40 
54.0 
2.7 
2.50 
1.75 
.70 
25 .. 
55 
38 
46.5 
2.7 
2.50 
1.75 
.70 
26 ... 
48 
30 
39.0 
2.7 
2.50 
1. 75 
.70 
27 .. 
53 
32 
42.5 
.4 
.43 
.30 
.12 
28 .. 
52 
28 
40.0 
1.2 
1.30 
1.60 
.12 
29 ___ 
58 
38 
48.0 
.3 
.21 
.16 
.30 
30 .. 
67 
38 
52.5 
.0 
.65 
.07 
.00 
31 . . .. 
59 
29 
44.0 
(«) 
(*) 
(°) 
(*) 
b 66.8 
b 34.4 
b 50.6 
• No record obtained. b Mean for the month. 
The decline was most marked after the minimum temperature of 
21° F. on December 10, and by December 13 the Deglet Noor and 
Zaheedy trees showed but a fraction of a millimeter in growth, proving 
that for the conditions in which they were at that period 21° was 
ve ry nearly a growth-inhibiting minimum. 
With the rise of the means from December 13 to 24 a little recovery 
was made in spite of several frosty nights, so that the depression in 
growth from December 26 and 27 practically to zero of growth on the 
