SOME RELATIONS BETWEEN THE GROWTH AND 
COMPOSITION OF YOUNG ORANGE TREES AND THE 
CONCENTRATION OF THE NUTRIENT SOLUTION 
EMPLOYED 1 
By H. S. Reed, Professor of Plant Physiology , and A. R. C. Haas, Assistant Pro - 
fessor of Plant Physiology , College of Agriculture } University of California 
INTRODUCTION 
The present paper is devoted to a discussion of the effects of different con¬ 
centrations of the nutrient medium upon young Valencia orange trees ( Citrus 
sinensis) and seedlings of the African sour orange (Citrus aurantium). 
THE RELATIVE CONSTANCY OF THE CONCENTRATION AND 
REACTION OF LEAF SAP 
The data on this point were obtained from young Valencia orange trees in 
cultures like those which have been previously described by the writers (3 ) 2 . 
The nutrient solutions applied were either Hoagland’s solution (3) or modifi¬ 
cations thereof. None were strongly toxic although growth was greatly retarded 
in certain series. Their osmotic concentrations as determined from the freezing- 
point depression ranged from 0.531 to 1.568 atmospheres, and their P H values 
ranged from 5.2 to 7.5. The plan of the experiments made it impracticable to 
determine the reaction of the nutrient solution after it was added to the sand 
cultures, but the reaction of the first 100 cc. of percolate collected after adding 
distilled water to the surface of the cultures was determined. The first drops 
collected had the highest P H values. All percolates had higher P H values than 
the nutrient solutions which had been applied. In the case of solutions which 
contained 1,000 parts per million of sodium bicarbonate (series 30-35 and 36-41) 
the P H of the percolates was approximately 8.3. The concentration of OH ions 
in the percolate from soil cultures which had previously received sodium chlorid 
solution was equally high. The replacement phenomena involved in such cases 
have been discussed by Cummins and Kelley (1). 
The data (Table I) show that the P H and concentration of the leaf sap from 
trees in the various cultures were remarkably uniform. The small differences 
found seem to bear no relation to the P H or to the concentration of the nutrient 
solution nor to the P H of the percolates. It appears that the absorption and 
metabolism of the orange trees produce a fairly constant reaction and concen¬ 
tration of the leaf sap. These results are not necessarily contradictory to those 
obtained by Haas (2) with the sap of Melilotus alba y where it was found that a 
gradient may exist in the plant. It is essential, however, that other plants be 
examined because any hypothesis based upon differences of acidity of the plant 
sap and the external medium must account not only for the accumulation of 
inorganic elements within the roots, but also for their movement to other 
portions of the plant in which different acidities may prevail. Moreover, the 
conditions of solubility in the root system may not be the same as those in other 
parts of the plant. 
i Received for publication Nov. 26, 1923, Paper No. 116, University of California, Graduate School of 
Tropical Agriculture and Citrus Experiment Station, Riverside, Calif. 
1 Reference is made by number (italic) to “Literature cited,” p. 284. 
Journal of Agricultural Research, 
Washington, D. C. 
( 277 ) 
Vol. XXVIII, No. 3, 
Apr. 19, 1924. 
Key No. Cal if.-37. 
