452 
Journal of Agricultural Research 
Vol. XXXI, No. 5 
overlapping leaf bases, with the accompanying fibrous sheath and 
lower down the outer zone of the trunk proper. Through these layers 
the air temperatures, cold or hot, penetrate very slowly and with 
considerable loss. 
(2) The ascending sap current , with a temperature acquired from 
the soil from which it is drawn by the roots. Under the insulation 
afforded by the protective layer and the outer portions of the trunk, 
the sap is able to reach the growth center at a temperature varying 
but a few degrees from that at which it left the soil, and so is able to 
neutralize much of either cold or heat, as the case may be, that has 
penetrated from without. 
It is believed that in the discovery of this stabilizing of the tempera¬ 
ture of the growth center of the date palm is disclosed a principle 
heretofore unrecognized in plant physiology, and one of vital impor¬ 
tance to palms and other endogenous plants in desert environments in 
enabling them to survive the extremes of their temperature exposures. 
LITERATURE CITED 
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1916. soil temperature. Mich. Agr. Exp. Sta. Tech. Bui. 26, 133 p. 
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1884. THE COURSE AND GROWTH OF THE FIBRO-VASCULAR BUNDLES IN 
palms. Proc. Amer. Phil. Soc. 21: 459-483, illus. 
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1916. HOURLY TRANSPIRATION RATE ON CLEAR DAYS AS DETERMINED BY 
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1855. g^ographie botanique raisonn^e. t. 1. Paris. 
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GO) - 
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(11) Lehenbauer, P. A. 
1914. GROWTH OF MAIZE SEEDLINGS IN RELATION TO TEMPERATURE. 
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(12) Livingston, B. E. 
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(13) - and Free, E. E. 
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(15) Martius, C. F. P. de 
[1850]. HISTORIA NATURALIS PALM ARUM. V. 1, illus. Lipsiae. 
