408 
Journal of Agricultural Research 
Vol. XXXI, No. 5 
ZERO POINT RECORDS AT SAN ANTONIO, TEX. 
Further evidence that the date palm zero point can not be above 
50° F., and a hint that for some varieties it may possibly he a little 
below that point, is found in the records secured on three seedling 
trees at the United States experiment farm at San Antonio, Tex., 
in March, 1917. 3 Table III shows temperature records of standard 
United States Weather Bureau thermometers and corresponding 
daily growth of one leaf on each of three 8-year-old seedling trees 
for the first seven days of March. 
Table III .—Temperature records and corresponding daily growth at San Antonio, 
Tex., of one leaf on each of three 8-year-old seedlings for March 1 to 7 
[Critical low temperatures are indicated in boldface type] 
Temperature 
Date 
Maxi¬ 
mum 
Mini¬ 
mum 
Mean 
Tree 1 
Tree 2 
Tree 3 
Mar. 1_ _ __ _ 
°F. 
74 
3 
o 
OJ? 
59 
Mm. 
20 
Mm. 
18 
Mm. 
14 
2 _ 
- jr ' 
63 
41 
47 
6 
4 
5 
3.... 
69 
41 
50 
3 
4 
3 
4... 
46 
32 
39 
3 
1 
2 
5. 
50 
22 
36 
2 
1 
1 
6 ... 
61 
31 
46 
2 
2 
2 
7... 
80 
46 
63 
1 
1 
1 
8 . 
70 
38 
64 
5 
3 
1 
9. 
73 
39 
56 
5 
5 
4 
10 . 
69 
68 
63 
9 
6 
4 
11 ... 
84 
64 
74 
21 
11 
13 
12 . 
81 
67 
74 
22 
12 
15 
Growth 
After a maximum of 75° F. on February 28 (fig. 3) the thermo¬ 
graph trace crossed the 50° line at 4 a. m. of March 1 and remained 
at 4° to 6° below it until 10 a. m. of March 2. It passed above the 
28 
u 
** / * 
1 ' l 
V 
1 
2 / 
1 
V v? > 
1 1 
V 
*? / 
& 
yo °^TA 
r\~~ 
— 
eo° 
- 
i 
r\ 
■50° - 
V 
1 
40° - 
-J 
30° - 
1 
1 
1 
1_ 
l 
M 
20° - 
r~ 
r~ 
\ 
\ 
\ 
\ 
\ 
\ 
\ 
Fig. 3.—Transcript from a thermograph record from February 28 to March 5,1917, at the United 
States experiment farm at San Antonio, Tex. The recording instruments were near the date 
palms from which the growth records in Table III were obtained 
50° line at noon March 2, ranging up to 59°, and dropping below it 
at 8 p. m. It remained below 50° throughout the 3d and 4th, 
dropping to 22° at 7 a. m. of the 5th, but reaching 50° at 11 a. m. 
* For the careful keeping of these records the writer is indebted to N. H. Mercier, of the Office of Western 
Irrigation Agriculture, Bureau of Plant Industry, U. S. Department of Agriculture. 
