Apr. i, 1921 
Growth and Sap Concentration 
95 
soil moisture present. During November and December there were 
light rains which did not penetrate deeply into the soil and did not affect 
the concentration of the cell sap of the trees. On January 4, 0.585 
inches of tain fell, and on the three succeeding days 5.2 acre-inches of 
irrigation water were applied. The effect of this increased supply of 
soil moisture is seen in the lower concentration of sap in the samples 
taken on January 29. The effect of the increased amount of water intake 
was to dilute the sap of the tree, even though active growth had ceased. 
SAP CONCENTRATION AND FRUITFULNESS 
The observations made upon these fruit trees may throw some addi¬ 
tional light upon the relationships between vegetative and fruiting 
activity of the tree. It appears that lower sap concentration is asso¬ 
ciated with abundant water intake and rapid growth. Severe pruning, 
which also stimulated ,active vegetative growth, caused pari passu , a 
lowering of the concentration of sap in the tree. 
Horticulturists have long recognized that those conditions which are 
associated with lower sap concentration are opposed to fruit bearing in 
a tree. With the data now in hand it seems possible to point out some 
additional relationships of interest. The most rapid growth occurs in 
the early part of the season. The apricot shoots in 1919 made about 
half of their total growth in the first one-fifth of their growing period. 
By the time that three-fourths of the length growth had been made, the 
sap concentration had reached a fairly high value, which was maintained 
during the remainder of the season. Now it is well known that this time 
of higher sap concentration is the time during which the fruit buds for the 
following year are developing on the tree. The various lines of evidence 
lead to the conclusion that higher sap concentration is associated with 
slower growth and fruit-bud formation. At the present time, however, 
it seems impossible to say which one of the conditions is cause and which 
is effect. Differences in the sap concentration of the stem at the apical 
and the basal ends of the shoots are so well marked as to be unmistak¬ 
able, yet it is somewhat difficult to orient one’s views to fit the facts. 
The sap concentration of entire shoots, including stems and leaves, was 
lower during periods of rapid growth and higher during periods of slower 
growth. Yet, when we note that the sap concentration of the rapidly 
growing apical region of the shoot was uniformly higher than that of the 
slowly growing basal region, the condition seems paradoxical. The con¬ 
dition seems the more paradoxical when one remembers that the apical 
portion of the stem has a higher water content and that the content of 
solutes must, therefore, be correspondingly higher in order to show a 
higher concentration in the expressed sap. 
We should remind ourselves, however, that growth is not wholly regu¬ 
lated by concentration per se. The composition of the sap, no less than 
