8 -—Ss- BULLETIN 271, U. S. DEPARTMENT OF AGRICULTURE. 
TABLE 9 [Swingle]—Sum of daily mean temperatures above 18° C. (64.4° F. \ forsee 
ing period of date palm from May i to October 31, at the stations a 
Sum of daily mean 
temperatures above 
18°C, Seen F.) from 
| May 1 to Oct. 31. 
Locality. | gf Remarks. 
| Degrees. | Degrees 
centigrade. f RaneennO 
Algiers, Algeria.....-.-------- 652 1,174 | No dates ripen here. 
Orleansville, Algeria..-.-.-.-. 788 1,418 | Very early sorts mature. 
Hresno Cale. ee see ee 1,054 1,897 | Average of many years’ observations. Daies of 
| sorts grown usually fail to ripen. 
MSICSONEPATAZ See Ses ers eee 1,409 2,538 | Average of 6 years’ observations. Dates of the 
| _ sorts now grown usually fail to ripen. 
Camo-Uoypt. 2 ser see ee 1,593 2, 868 | Dates ripen regularly. ; 
Phoenix, Ariz. (Salt River 1,677 3,019 | Average of many years’ observations. Many 
_ Valley). sorts of Gates ripen regularly. 
Biskra, Algeria (Northern 1,86 3,304 | Average of 10 years’ observations. Many sorts 
; ing industry. Deglet Noor dates ripen but 
are not of the best quality. 
Ayata, Algeria, 1890 (Oued 1,816 3, 269 
Sahara). of dates ripen regularly; date culture the lead- 
Deglet Noor dates ripened very imperfectly. 
Rirh region), Sahara. : 
=Avyata ARGU Sono ceases oe 1,906 3,431 | Deglet Noor dates ripened very slowly and im- 
periectly. 
Aya, 1889 5a eee Se 2,091 3,764 | Deglet Noor dates ripened well. 
Tougourt, Algeria (Oued 2,049 3 689 | Do. 
Rirh region). 
Bagdad, Mesopotamia.-.---.--- 2,356 4,242 | Average of 5 years’ observations. Many excel- 
lent varieties ripen. 
Indio, Cal. (Salton Basin)..... | 2, 237 4,027 | Average of several years’ observations. 
Indio, IQS yess Se eee 2,348 4,227 | New thermometers. 
Mammoth Tank, Cal. (Salion | 2,585 4,652 | Average of 23 years’ observations. 
asin) : . 
Salton, Cal., 1903 (Salton 2,074 3,734 | Fhe coolest summer recorded. Observations 
Basin). | taken for the first time with standard Weather 
Bureau thermometers in the regulation shel- 
: ters. 
Salton anGan .. 2-55-55. 35. =<= 2,679 4,823 | Average of 12 years’ observations. 
Salion al sO 7sss ws se 3,392 6,106 | Hottest summer recorded ai Salton. 
Salton slG02s se eee ee eS 2,749 4,948 
Imperial, Cal., 1902 (Salton 2,106 3, 791 
Basin). 
In those calculations 64.4° F. is assumed as the zero point of 
activity of the date tree as far as flowering and fruiting functions 
are concerned, any number of degrees of daily mean temperature 
above that point being available to the tree in forwarding its fruiting 
functions, though growth of leaves and stem may go on at tempera- 
tures considerably lower. 
By multiplying the number of degrees above 64.4 in any monthly 
mean by the number of days of that month the number of available 
heat units (1 degree 1 day) is arrived at. The summations for the 
months of May to October, inclusive, in column 5 of Table I have 
been arranged for comparison with those of the table quoted from 
Swingle. 
The summations of 2,049 heat units for Alexandria and 2,179 units 
for Gizeh must be fairly representative of the conditions under which 
the greater number of the date trees of the five varieties mentioned 
make their growth. (Pl.II.) By comparison with table 9 of Bulletin 
No. 53, referred to, it will be seen that localities having such low sum- . 
mations are not counted in the possible date-growing territory, except 
