OSMOTIC CONCENTRATION OF LEAF SAP 273 
cated by actual measurements occasionally, just as in other 
instances the increase indicated by the constants would be higher 
than the true value.* 
III. PRESENTATION AND ANALYSIS OF DATA 
Altogether 26 sets of determinations were made, covering 12 
species of trees. All collections were made in the immediate 
neighborhood of the Station for Experimental Evolution. The 
results are given in the accompanying tabular statement. 
Here are given the approximate actual heights above the 
ground of the samples of leaves taken, designated by letters A, B, 
C, --+ from the highest to the lowest, the depression of the freezing 
point, A, and the osmotic concentration or pressure in atmos- 
pheres, P, specific electrical conductivities, x, multiplied by 10° 
and x/A X 10° of the expressed leaf sap. 
These results in terms of osmotic concentration, P, are repre- 
sented in DIAGRAMS I and 2, which are self-explanatory. 
A cursory examination of the protocol or a glance at the 
diagrams shows that almost without exception the osmotic con- 
centration is higher in samples taken at the higher levels. 
As a means of more exact comparison we have determined the 
difference in these values for every possible pair of levels, i. e., 
1/2n(n — 1) sets of differences for each tree, where is the number 
of levels from which samples were taken. These differences are 
taken (constant for higher level) less (constant for lower level). 
* A particular case in point is that of two determinations based on a tree of 
Populus balsamifera. A first pair of collections made on August 25, indicated that 
that of leaves from the 25-foot level. A repetition of the collections on August 28 
indicated that the sap of the leaves from the 22-foot level froze 0.105° higher—i. e., 
had 1.26 atmospheres ——, —— Spa ARR cage em at the 6-foot level. 
Note that if thes hey indicate a higher osmotic 
concentration for the samples taken at the tighes ne Since, however, the two 
not consistent we have omitted both. ead this tree mie not have been 
newt = at since chit: pollectiqns irom the lower branches were made from the ends of 
e from ne aintrunk. Thus ifthe resistance 
of the conducting tracts be a factor of ake it would tend to minimize the 
a * between the two determinations. 
o of the determinations based on Juglans and in twoor more of those 
based on pais collections were made from the same trees in 1914 and I9I5. 
Otherwise all are based on different individuals. 
