468 
Journal of Agricultural Research 
Vol. XXXI, No. 5 
It must be concluded, then, that the inhibiting of the date-pjalm 
leaf growth in intense sunlight of the desert regions is due chiefly 
to the action of rays of wave length from about 0.57 jx in the yellow 
to about 0.405/x in the violet end of the visible spectrum, but invisible 
ultra-violet rays probably assist in stopping growth. 
Photosynthesis is most active in longer wave lengths from the line 
D at the end of the yellow to lines B and C in the red; thus growth 
is inhibited by light that has but little potency in photosynthesis 
and conversely carbon assimilation is favored by light that has but 
little ability in inhibiting growth. 
Growth in absence of direct sunlight is apparently synchronous 
with the closing of the stomates, checking of transpiration, and in¬ 
creased turgescence in the meristematic tissue* 
LITERATURE CITED 
(1) Branner, J. C. 
1884. THE COURSE AND GROWTH OF THE FIBRO-VASCULAR BUNDLES IN 
palms. Proc. Amer. Phil. Soc. 21: 459-483, illus. 
(2) Fowle, F. E. 
1923. smithsonian physical tables. Ed. 7 rev., reprint 2. Smithsn. 
Misc. Collect., v. 71, no. 1, 458 p. 
(3) Gray, J., and Peirce, G. J. 
1919. THE INFLUENCE OF LIGHT UPON THE ACTION OF STOMATA AND ITS 
RELATION TO THE TRANSPIRATION OF CERTAIN GRAINS. Amer. 
Jour. Bot. 6:131-155, illus. 
(4) Jost, L. 
1907. lectures on plant physiology. Translated by R. J. H. Gibson. 
564 p., illus. Oxford. 
(5) Mason, S. C. 
1915. BOTANICAL CHARACTERS OF THE LEAVES OF THE DATE PALM USED 
IN DISTINGUISHING CULTIVATED VARIETIES. U. S. Dept. Agr. 
Bul. 223, 28 p., illus. 
( 6 ) - 
1925. THE MINIMUM TEMPERATURE FOR GROWTH OF THE DATE PALM AND 
the absence of a resting period. Jour. Agr. Research 31: 
401-414, illus. 
(7) - 
1925. PARTIAL THERMOSTASY OF THE GROWTH CENTER OF THE DATE PALM. 
Jour. Agr. Research 31: 415-453, illus. 
(8) Palladin, V. I. 
1923. plant physiology. Ed. 2 (Amer.) by B. E. Livingston. 360 p., 
illus. Philadelphia. 
(9) Reinke, J. 
1884. UNTERSU CHUN GEN UBER DIE EINWIRKUNG DES LICHTES AUF DIE 
SAUERSTOFFAUSSCHEIDUNG DER PFLANZEN. Bot. Ztg. 42:1-10, 
17-29, 33-46, 49-59, illus. 
(10) Swingle, W. T. 
1904. THE DATE PALM AND ITS UTILIZATION IN THE SOUTHWESTERN STATES. 
: U. S. Dept. Agr., Bur. Plant Indus. Bul. 53, 155 p., illus. 
