Apr. i, 1921 
Growth and Sap Concentration 
85 
correlation shows that when growth is rapid the sap concentration is 
lower and when growth is slower the sap concentration is higher. 
These conclusions may be verified by inspection of the figures in Table 
I. For example, an increment of 15 cm. in the week ending July 23 
coincided with a sap concentration of 10.4 atmospheres, while smaller 
increments coincided usually with higher sap concentrations. The 
small growth increments in the latter part of the season are accompanied 
by the highest concentrations of plant sap. The concentration of 
solutes in the sap tends to increase with age of the leaf, as Dixon and 
Atkins (j) discovered in the study of Ilex. 
GROWTH INCREMENTS AND SAP CONCENTRATION OF YOUNG 
APRICOT TREES (1918) 
The question of sap concentration in shoots of young apricot trees 
in relation to growth was also investigated. The trees from which the 
material was obtained had been growing in the orchard two years when 
these studies were started. Soon after the season’s growth began, 70 
young shoots were selected and marked with labels. An India ink 
mark was made near the base of each shoot, from which length measure¬ 
ments were made at intervals of seven days. At the time of making the 
measurements here recorded a sample of shoots was collected from adja¬ 
cent trees, and these samples were used for determining the sap concen¬ 
tration. The samples consisted of entire shoots of that particular 
season’s growth. The stems and leaves were ground together, and the sap 
was expressed. The samples were given a preliminary freezing and 
were treated essentially as the walnut samples were treated. 
The growth and sap concentration determinations made in 1918 upon 
apricot shoots are given in Table II. It will be noted that where the 
intervals were not exactly seven days the increments were calculated to a 
7-day basis in order to make them comparable. It will be noted that the 
rate of growth was greatest at the outset of the observations and dimin¬ 
ished with several fluctuations to the end of the growing season. Certain 
dynamical aspects of this growth rate have been discussed in a separate 
paper (11) though the studies there related were based upon another set of 
measurements. 
The concentration of the cell sap (expressed in atmospheres of osmotic 
pressure), although subject to some fluctuation, increased as the season 
advanced. The lowest concentration was observed on May 21 and 
the highest on October 31. The average osmotic pressure, expressed 
in atmospheres by months, is: May, 11.84; June, 13.66; July, 14.34; 
August, 15.04; September, 15.18; October, 16.48. Table II shows that 
the concentration of the sap, which was 12.71 atmospheies on May 2, fell 
to 10.87 i* 1 the next three weeks, simultaneously with rapid elongation of 
the shoots. The concentration at once began to rise and went up, with 
some irregularities, to 18.90 atmospheres on October 31. 
