Apr. i, 1921 
Growth and Sap Concentration 
89 
dynamical features of the growth rate of these trees have been de¬ 
scribed in another paper ( 13 ) and will not be discussed here. 
The concentration of the cell sap of the two classes of shoots fell off 
somewhat after the observations were started, then rose, although fluc¬ 
tuating, toward the end of the growing season. The concentration of the 
sap of the slower shoots on the unpruned trees was generally higher during 
the season than that of the rapidly growing shoots on the heavily pruned 
trees, although at the end of the season the sap of the two classes was 
substantially similar in concentration. Thus, both comparisons show 
that a higher concentration of cell sap is found in slower growing shoots. 
Fig. 3.—Graph showing regression of osmotic pressure on growth increments of unprunetl apricot trees 
(1919)' 
In order to measure the association between growth and sap concen¬ 
tration I shall employ the correlation coefficient. 
The correlation between concentration of cell sap and inclement in 
length is 
I. r— — o.628±o.o88 for heavily pruned trees. 
II.r= —0.823±0.049 f° r unpruned trees. 
Reference to figures 3 and 4 shows that regression in the pruned 
trees is fairly linear, but in the unpruned trees this linearity is doubtful. 
In the latter case, the significance of the correlation coefficient may be 
more apparent than real. 
It will be readily recognized that factors which contribute to the higher 
sap concentration of the unpruned trees are associated with the nature 
of the growth they made. Their slower growth and consequent dimin¬ 
ished draft on the plastic materials of the tree should allow a greater 
