Sept. 1, 1925 
Minimum Temperature for Growth of Date Palm 
407 
Table II .—Leaf growth record of date palms at Indio , Calif., January , 1917 
[Critical low temperatures and approximation to zero of growth are indicated by boldface type] 
Temperature 
Average leaf growth per day 
Date 
Maxi¬ 
mum 
Mini¬ 
mum 
Mean 
Asherasi 
Deglet 
Noor 
Thoory 
Zaheedy 
Jan. 1_____ 
o p 
62 
o p 
34 
o F 
48.0 
Mm. 
1.03 
Mm. 
0.85 
Mm. 
0.70 
Mm. 
0.56 
2..... 
63 
39 
51.0 
.93 
1.43 
1.25 
.56 
3.... 
57 
42 
49.5 
1.40 
.91 
1.00 
.00 
4...... 
64 
28 
46.0 
.93 
1.07 
.33 
.00 
5.... 
64 
32 
48.0 
.43 
1.43 
.66 
.31 
6.... 
64 
37 
50.5 
1.30 
.64 
.90 
.50 
7__ 
64 
33 
48.5 
.50 
.00 
.00 
.00 
8... 
60 
43 
51.5 
1.00 
.71 
.25 
.80 
9.... 
76 
44 
60.0 
1.40 
1.21 
1.33 
.30 
10... 
80 
47 
63.5 
2.20 
1.43 
1.16 
.62 
11.... 
75 
37 
56.0 
2.40 
2.60 
1.90 
.94 
12__ 
77 
39 
58.0 
3.40 
3.70 
1.90 
1.56 
13__ 
65 
48 
56.5 
4.30 
4.00 
2.00 
1.30 
14__ 
69 
29 
49.0 
3.40 
4.00 
2.80 
1.30 
15.... 
55 
36 
45.5 
2. 30 
4.40 
2.76 
1.30 
16.... 
50 
84 
42.0 
2.14 
1.86 
1.83 
.87 
17... 
50 
88 
44.0 
1.60 
1.50 
1.83 
.81 
18.... 
46 
33 
39.5 
.50 
.64 
.66 
.00 
19___ 
49 
44 
46.5 
.00 
.50 
.33 
.00 
20..... 
56 
34 
45.0 
.00 
.43 
.50 
.00 
21____ 
60 
32 
46.0 
.50 
.00 
.00 
.00 
22 .... 
58 
33 
45.5 
1.20 
1.30 
1.16 
.30 
23.... 
60 
30 
45.0 
.14 
.80 
.75 
.25 
24.. 
65 
30 
47.5 
.50 
.64 
.75 
.25 
25.... 
66 
28 
47.0 
.50 
.70 
.93 
.00 
26...— _ 
71 
34 
52.5 
1.20 
.84 
.44 
.50 
27___ 
70 
34 
52.0 
.90 
.72 
.44 
.50 
28.... 
66 
31 
48.5 
1.26 
1.10 
.38 
.40 
29____ 
70 
32 
51.0 
1.80 
1.50 
.87 
.80 
30______ 
69 
33 
51.0 
2.10 
2.00 
1.20 
.60 
31... 
70 
48 
59.0 
1.50 
2.00 
1.20 
1.00 
«63.6 
° 36 
<*49.8 
• Mean for month. 
The tardiness of the Deglet Noor and Thoory trees in coming 
to f ull cessation of growth, with the fact that the Deglet Noor main¬ 
tained some slight gain throughout the December period; suggests 
that if 50° F. is the zero point for the Zaheedy seedling, which 
represents the more tender Persian Gulf varieties. Deglet Noor and 
Thoory may have a zero point a little lower, possibly 48°; for it is 
to be expected that within the range of individuals and varieties of 
Phoenix dactylijera there may be a zero point difference of several 
degrees. 
Again the thermograph sheet shows the actual time of exposure 
of these trees to the low maximum. 
Indio Thermograph Record, January 15-21, 1917 
On January 15, after the temperature had been below 50° F. since 
5 p. m. of the 14th, the maximum was 50° to 52° (maximum ther¬ 
mometer 55°) from 10 a. m. until about 1.30 or 2 p. m. From that 
time the temperature was 50° or below until noon of the 20th, giving 
a total as follows: 
Summation, 50° or below: Hours 
January 15_ 10 
January 16_ 24 
January 17_ 24 
January 18_ 24 
January 19_ 24 
January 20_ 12 
Total_ 118 
