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Journal of Agricultural Research 
Vol. XXXI, No. 5 
(2) Balanced against the first, the influence of the ascending sap 
current, deriving its temperature from the soil at the depth of the 
greater mass of the absorbing roots, hence subject to but moderate 
fluctuations. It was recognized that this sap current might exert 
a cooling or a warming influence on the general body temperature 
of the plant according to whether it was of a lower or higher tempera¬ 
ture than that derived from the air; becoming a cooling influence in 
the summer, a warming one in the winter. 
(3) Interposed between the external air and the trunk interior, 
DeCandolle recognized the insulating value of the bark and the 
woody trunk, resiting the penetration of the exterior heat or cold 
on the one hand; blanketing and conserving the temperature of the 
ascending sap on the other. 
(4) The importance of leaf transpiration in inducing the flow of 
the sap current was recognized when the top was removed from the 
tree in Rameaux’s experiment, the rise of the trunk temperature 
when exposed to the sun being attributed to the absence of the cool¬ 
ing sap current ascending at soil temperature. 
Influence of the interior temperature on the growth centers and 
cambium is nowhere suggested, nor was there any recognition of the 
giant buds which characterized such genera as palms, yuccas and 
Dracenas, nor of the specially insulating layers which surround such 
buds in the date palm. 
LIMITATION OF THE GEOGRAPHICAL RANGE OF THE DATE 
PALM BY TEMPERATURE 
The geographical occurrence of the date palm must be considered 
under two categories. 
(1) THE ARTIFICIAL OR PLANTING RANGE 
The artificial or planting range in which the date palm will survive 
is a much wider one than the range of fertile seed: production and 
must be limited by such a degree and duration of cold as would 
enable frost to reach the meristematic tissues of the growth center. 
It has been shown in previous pages that growth was not wholly 
checked by minimum temperatures above 21° or 22° F. of short 
duration, but many hundreds of palms in the Coachella Valley 
of California survived minimum temperatures of 13° to 15° 
January 7 and 8, 1913, with only a severe killing of the leaves. 
At the United States Experiment Station at Sacaton, Ariz., this 
same cold spell gave minimum temperatures, January 6, 9°; January 
7, 10°; and January 8, 11°; with similar results, a severe freezing of 
leaves, but the growth center unharmed. In San Antonio, Tex., 
previously referred to, mature palms have survived minimum tem¬ 
peratures of 4°, though all foliage was killed. The short duration of 
the severe cold would have had little effect on the soil temperature 
penetrated by the roots and the latent heat of the sluggish sap 
current must have been able to overcome the penetration of cold 
toward the bud. 
(2) THE NATURAL OR SEED PRODUCTION RANGE 
The natural or seed production range of the date palm would be 
within a climatic area which would permit the production of viable 
seeds for the propagation of the species. This lies far inside the area 
