GROWTH AND SAP CONCENTRATION 1 
By Howard S. REEd, 3 Professor of Plant Physiology, University of California 
Chandler (r) 3 found that trees making rapid growth had lower sap 
concentration and that slower growth of the tree was accompanied by 
higher concentration. Trees which made rapid growth as a result of 
severe pruning in the preceding winter had a lower concentration of 
sap than trees which had been lightly pruned. During the summer 
season the concentration of the cell sap was lowest near the ground and 
highest in the upper part of the tree. Although Chandler’s method 
of preparing the samples for freezing-point determinations has been 
adversely criticized, one must acknowledge the advance he made in our 
knowledge of sap concentrations in fruit trees. 
Dixon and Atkins (5) observed that the sap of young leaves of various 
plants had, as a rule, a lower osmotic pressure than sap from mature 
leaves. 
Lutman (ro) has determined the freezing-point depressions of the sap 
of the potato plant with reference to its growth cycles. The variations of 
concentration seem to be related to the development and rate of growth 
of the plant. 
The seed tubers when taken from storage had a relatively high osmotic 
pressure, but as water was absorbed the osmotic pressure dropped. As 
the age of the plant increases its osmotic pressure increases on account 
of the accumulation of inorganic salts in its cells; but when senility begins, 
the osmotic pressure drops, because of the loss of soluble materials. In 
the young plant the leaf sap is more concentrated than the stalk sap, but 
after the flower buds are put out and the tubers begin to grow, the stalk 
sap is more concentrated. With the advent of cool, rainy weather later 
in the season the leaves begin to grow again and their sap concentration 
is greater than that of the stalks. Shading the potato plant diminishes 
the osmotic pressure of the leaves and stalk. 
Synopses of the earlier literature dealing with cryoscopic methods and 
with the relation of the physical environment to the concentration of 
the cell sap will be found in the summaries prepared by Dixon (2), Hib¬ 
bard and Harrington (7), and Harris and Lawrence (5). 
1 Paper No. 71, University of California, Graduate School of Tropical Agriculture and Citrus Experiment 
station, Riverside, Calif. 
s It is a pleasure to acknowledge the aid which has been rendered by those associated with the progress 
of this work. The author's thanks are due to Messrs. L. C. Masters, R. H. Holland, and F. F. Halma. 
• Reference is made by number (italic) to "literature dted," p. 98. 
Journal of Agricultural Research, 
Washington, D. C. 
xb 
(81) 
Vol. XXI, No. 1 
Apr. 1, 1921 
Key No. Calif.-*g 
