8 4 
Vol. XXI, No. i 
Journal of Agricultural Research 
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The samples collected for freezing-point determinations always con¬ 
sisted of the total growth of a shoot of that particular season (ab initio) 
and included both stems and leaves. Toward the end of the growing 
season the stems were large and woody; nevertheless they were ground 
in the handmill and pressed like the other material. Most of the sap 
so obtained came undoubtedly from the cortical layers of the stems. 
By referring to Table I the reader will see the nature of the results 
obtained in this work. The table shows the mean height of the trees 
(from the basal ink mark), the height increment from the preceding 
measurement, and the concentration of the cell sap expressed in atmo¬ 
spheres of osmotic pressure. The mean height increased from 62 cm. 
on June 12 to 201.2 cm. on October 29. The increments (calculated in 
each case to a 7-day basis) were far from uniform, ranging as they do 
from 0.7 cm. to 15 cm. The atmospheres of osmotic pressure of expressed 
sap range from 8.9 to 24.4. Thus it will be seen that there are periodic 
variations in the concentration of the cell sap and in the growth rate 
from week to week during the season. The maximum growth rate was 
observed during certain weeks in July, and the maximum osmotic pres¬ 
sure of the cell sap was observed near the end of the growing season- 
It is somewhat difficult to get a comprehensive idea of the relation¬ 
ship between growth and sap concentration from the array of figures 
given in Table I. It will be better to investigate the nature and amount 
of the mathematical correlation between the two sets of values. There 
are 19 observations in which both the increments and sap concentration 
were determined. While this number is rather scanty for determining 
correlation, the regression is remarkably linear (fig. 1), and it is believed 
that the correlation coefficient is trustworthy. The coefficient of corre¬ 
lation between the two variables is -o.557io.113. The negative 
