416 
Journal of Agricultural Research 
Vol. XXXI. No. 5 
hemisphere, and indicate the range of temperature and humidity 
which may be encountered. 
Temperature and humidity ranges in the date-growing region of 
the Nile Valley, from Alexandria and Rosetta on the Mediterranean 
coast to Khartoum, comprising a practically continuous north-and- 
south extension of this culture for over 1,000 miles, were shown in 
diagrams and discussed by the writer in 1914 {16). 
Port Said and Alexandria represent in their monthly means of 
from 56° to 80° F. about the lowest temperatures at which com¬ 
mercial date culture may hope to succeed, here accompanied by high 
humidity, with monthly means of from 64 per cent to 76 per cent 
throughout the year. Merowe and Atbara in Sudan have nearly 
the upper temperature limits at which date culture may be conducted, 
with monthly means of 68° in January and 93° in June. The rela¬ 
tive humidity at Merowe is the lowest recorded for a date-producing 
region, with means on a 15-year record of only 12 to 16 per cent from 
March to June and an annual mean of 22 per cent. 
But even with the great range of adaptability as seen in Egypt, 
the full measure of adjustment to temperature of which this tree is 
capable is not attained. In the Salt River and Gila River Valleys 
of Arizona date palms have survived minimum temperatures of from 
9° to 11° F. with the loss of only the exposed leaves, then, pushing 
up new leaves promptly with the return of warmer weather, have 
produced abundant crops of fruit in the year following. Nonfruiting 
seedling date palms in San Antonio, Tex., have survived minimum 
temperatures of 4° F. with continuous temperatures below the freez¬ 
ing point for more than 48 hours. At the other extreme, maximum 
temperatures of 121° at the United States Date Garden at India, 
Calif., have not seriously impeded the growth rate of the leaves of 
young date palms nor impaired the development of their fruit. 
Such facts regarding a tree of the first economic importance in¬ 
vite the closest study of any peculiarities in its anatomical structure 
and physiological action which may enable it to endure such vicis¬ 
situdes. The Arab’s idea of the wants of the date palm, “Its feet 
in running water, its head in the fire of the sky, ” has so often been 
repeated, that the growing of the tree under such conditions has been 
accepted as a matter of course. No one seems to have been aware 
.that the widespread, powerful root system, the sturdy and lofty 
trunk, capped by the single giant bud with its deeply seated growing 
point, and majestic crown of a hundred leaves, together comprise a 
remarkable provision of nature for the protection of the embryonic 
cell tissues against wide extremes of both heat and cold, and furnish 
a stabilizer of growing-point temperatures for this tree of the desert. 
Like all palms, the date palm is endogenous, its growth internal, 
with no sensitive cambium zone to be exposed to sunscald under the 
desert heat. Like all but a small group of palms, it has an un¬ 
branched cylindrical trunk, the product of the perennial intercalary 
growth of a single terminal bud, which in this species is of enormous 
size. 
De Candolle (J, p. 37) had the impression that the date palm has 
a distinct dormant or resting period after its fruit is matured and 
during the winter months, and he speculated concerning the tem- 
3 Reference is made by number (italic) to **Literature cited/' p. 462. 
