Apr. i, 1921 
Growth and Sap Concentration 
3 : 
EFFECT OF PRUNING UPON SAP CONCENTRATION 
The results obtained from determinations on the walnut and apricot 
trees are interesting and seem conclusive so far as they go, but they raise 
other questions which seem worthy of study. 
In pursuance of these inquiries, determinations were made on the same 
block of apricot trees throughout the season of 1919. The growth and 
sap concentration were determined on two lots of trees, one of which is 
heavily pruned each winter while the other is not pruned at all. Need¬ 
less to say, the growth of individual shoots on the heavily pruned tree, 
was much greater than that of shoots on the unpruned trees. 
The mean length of shoots was determined at weekly intervals, as 
before. In the beginning, 50 shoots were selected on each lot of trees, 
Fig. 2. Graph showing regression of osmotic pressure on growth increments of apricot trees (1918). 
but, as a result of breakage and other accidents, a number had to be 
eliminated. The computations are based on 33 shoots on the unpruned 
trees and on 28 shoots on the heavily pruned trees. The evaporating 
power of the air was determined by the evaporation of distilled water 
from a white, spherical atmometer bulb supported on a stand 5 feet 
from the ground in the center of the orchard. The average daily tem¬ 
perature was taken from the Riverside official reports, which were 
obtained from standard instruments located about 2 miles distant. The 
soil moisture was determined from composite samples taken to a depth 
of 3 feet throughout the area occupied by the trees in question. The 
sap concentration was determined by the depression of the freezing 
point. 
A summary of the several factors is shown‘in Table III. 
