Vol. 44 No. 6. 
BULLETIN 
OF THE 
TORREY BOTANICAL CLUB 
—_ + 
JUNE, 1917 
The relationship between the osmotic concentration of leaf sap and 
height of leaf insertion in trees 
J. ARTHUR Harris, Ross AIKEN GORTNER, AND JOHN V. LAWRENCE 
(WITH FOUR DIAGRAMS) 
I. INTRODUCTION 
The ascent of sap in trees presents a problem of such com- 
plexity that no one kind of observation is sufficient for its solution. 
Final conclusions must be based upon the comparison and correla- 
tion of careful measurements of all possible variables. 
The réle to be attributed to the osmotic concentration of the 
fluids of the leaf cells, like other possible factors in the rise of 
the transpiration stream, is still subject to marked differences 
of opinion. 
One of the simplest and most direct methods of approaching 
the problem of the relationship between the concentration of the 
leaf sap and the movement of the transpiration stream is to deter- 
mine whether leaves originating at a greater distance from the 
source of water absorption exhibit a higher osmotic concentration 
than those inserted nearer the source of intake. The importance 
of such determinations has been recognized by Ewart, Dixon and 
Atkins, Hannig and others. 
Ewart was one of the first, if not the first, to attempt the deter- 
mination of the osmotic concentration of the leaf sap at different 
levels. In 1905 he* thought he had demonstrated by plasmolytic 
methods that the concentration of the leaf sap increases from 
[The BULLETIN for May (44: 229-266. pl. 9-16) wa issued May 22, 1917.] 
* Ewart, A. J. The ascent of water in trees. Phil. Trans. Roy. Soc. Lond. B. 
198: 41-86. 1905. 
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