Apr. i, 1921 
Growth and Sap Concentration 
93 
Sap-concentration determinations were made upon each of these sam¬ 
ples separately. The concentrations expressed as atmospheres of osmotic 
pressure were as follows: 
A. i3-*9 
.. IX - 81 
... . IO * 97 
.. IO - 3 2 
CONCENTRATION OF SAP IN ORANGE SHOOTS AND LEAVES 
The leaves of the orange tree persist for more than one year. New 
shoots commonly arise from axillary buds and may attain considerable 
length before the subtending leaf falls. Determinations were made of 
the sap concentration in new shoots of the Washington Navel orange and 
of the old leaves subtending them. The leaves had grown to maturity 
in the summer preceding the appearance of the shoots and might be 
supposed to have some physiological relation to their axillary shoots. 
Fio. 6 .—Graph showing seasonal changes in sap concentration in orange shoots and their subtending leaves. 
0 =sap concentration of young shoots. 
□—sap concentration of the subtending leaves. 
There was, however, no general relationship indicated by the sap con¬ 
centration of the two members. Figure 6 represents graphically the 
changes in sap concentration of leaves and their axillary shoots from 
April 15 to October 9. During the first few weeks the sap concentra¬ 
tion of the stem appeared to fluctuate and reached the low point for the 
season about May 1. From May until October there was a general 
tendency for the sap concentration to rise, though not to so marked a 
degree as was seen in the apricot. Throughout most of the summer the 
concentration of the leaf sap was greater than that of the shoot sap. 
The mean of the determinations of the leaf sap was 18.4 atmospheres 
and of the shoot sap 17.3 atmospheres. 
The root-mean-square deviation of a series of values from their mean, 
as stated above, is an excellent measure of their dispersion. In this case 
the root-mean-square deviation of the leaf-sap concentration is 1.21 
atmospheres and that of the shoot sap is 1.64 atmospheres. This shows 
that the concentration of sap in the leaves was subject to slightly less 
