96 
Journal of Agricultural Research 
Vol. XXI, No. i 
its total concentration, affects the activity of the cell. Attention has 
recently been called to the effect on plant growth of inhibiting substances 
resembling chalones (9, 14). The absence of these growth-inhibiting 
substances in the apical portion of the shoot accounts in large measure 
for the more rapid growth of that region. There are also numerous 
lines of evidence which indicate that the sap of the apical region of the 
stem promotes vegetative growth because of its greater content of nitrog¬ 
enous substances, while the slowly growing basal portion of the shoot 
is favorable to fruit-bud formation because of its greater content of car¬ 
bohydrates ( 8 ). It goes without saying that we must recognize qualita¬ 
tive as well as quantitative differences in the plant sap in analyzing its 
Fig. 7. —Graph showing growth and sap concentration of Golden Nugget navel oranges. Average weight 
of fruits is shown by solid lines, sap concentration of fruits by broken line. 
effects on growth. The evidence, however, indicates that an increasing 
sap concentration in the shoot as a whole retards vegetative growth, 
while a decrease in the sap concentration of the whole shoot favors growth. 
SAP CONCENTRATION AND THE GROWTH OF ORANGE FRUITS 
The orange fruit was selected for study because it has a relatively long 
period of growth and develops on a tree which continuously bears green 
foliage. The variety employed is a strain of the navel orange known 
as “Golden Nugget.” Determinations began on June 5, 1918, and were 
continued at weekly intervals until January 16, 1919. The mean weight 
of fruits on the former date was 0.39 gm. The growth rate was rather 
slow from the beginning of the observations until the end of the ninth 
