Apr. i, 1921 
97 
Growth and Sap Concentration 
week; then a period of more rapid growth set in, which lasted until the 
twenty-sixth week (Dec. 1). Toward the close of the period there was 
considerable fluctuation in the weight of fruits, largely because of errors 
in sampling, but the final mean weight was somewhat over 200 gm. The 
courses of the growth process and of the sap concentration of the fruit 
are shown in figure 7. During the first nine weeks, while the fruits were'" 
growing slowly, their sap concentration varied between 12 and 14 atmos¬ 
pheres of osmotic pressure. When more rapid growth began, the sap 
concentration dropped to a pressure between n and 12 atmospheres, 
but subsequently gradually rose. As the fruit approached maturity 
there was a great increase in its sugar content and a consequent increase 
in the concentration of the sap. 
During the first half of the growth period it is quite evident that rapid 
growth is accompanied by a lower sap concentration. In the latter half 
of the growth period it is more difficult to ascertain the relationships 
between sap concentration and growth because of the fact that while the 
fruit is still growing it begins to accumulate increasing amounts of soluble 
carbohydrate. 
SUMMARY 
(1) Observations on the growth and sap concentration of young trees 
showed that the two variables have a tendency to vary in opposite direc¬ 
tions—that is to say, rapid growth is associated with a generally lower 
concentration of sap in that shoot, while slower growth is accompanied 
by higher concentrations of sap. 
(2) There was a gradual increase in sap concentration as the season 
advanced. In apricot trees the concentration continued to increase for 
some time after active growth had ceased. The accumulations of solutes 
in the plant sap is unquestionably related to the synthetic metabolism 
of the tree as the season advanced, though there is some evidence that 
diminished water absorption was partially responsible for the increased 
sap concentration. 
(3) Of several environmental factors measured, soil moisture was the 
only one having an obvious effect upon sap concentration. The addition 
of water to the soil usually diminished the concentration of the plant 
sap. 
(4) The sap concentration of shoots on trees heavily pruned was lower 
than that of shoots on trees not pruned, because of the more rapid 
growth of the former. 
(5) A concentration gradient appears to exist in the shoot. The con¬ 
centration of the sap in the apical portion of a stem was greater than that 
in the basal region. The sap concentration in the stems showed a greater 
tendency to fluctuate than that in the leaves. 
(6) Lower concentrations of plant sap in the shoot as a whole appear 
to be associated with abundant water intake and rapid vegetative growth. 
