Mar., 1923] 
BARTHOLOMEW — INTERNAL DECLINE 
125 
Acidity 
It was found in studying the acidity of the lemons that, while the total 
acid content increases as the size of the lemon increases, the true acidity 
of the juice, like the water content, increases comparatively little after the 
lemon has reached a diameter of about 3.8 cm. By referring to table 1 it 
will be seen that in this series, lemons averaging 3.63 cm. in diameter showed 
average pH values of 2.54 for the stylar end and 2.50 for the stem end, 
while 5 months later, when the lemons in this same series had attained 
an average diameter of 5.18 cm., the pH values were only 2.29 and 2.33. 
In another series, when the average diameter was 4.32 cm., the pH values 
were 2.57 and 2.54. Eight months later the average diameter had increased 
to 5.72 cm., but the acidities had increased only to pH 2.33 and 2.36. These 
two examples are typical of all the series. 
Lemons which are all approximately of the same age and size show a 
great deal of individual variation in acidity. For example, mature lemons 
taken from storage and tested individually showed variations in acidity 
such as the following: pH 2.27, 2.40, 2.37, 2.29. 
The average acidity obtained for all the mature lemons tested was 
pH 2.31. This value is somewhat lower than it would have been had the 
tests been made on first-class market lemons. Some of the lemons tested 
in this work had been allowed to remain on the trees until they were in the 
condition known to the growers and packers as tree-ripe. 3 When lemons 
have reached this condition they have a slightly higher sugar and slightly 
lower acid content than earlier. 
Variations in acidity were found not only in individual lemons but in the 
different ends of the same lemons. In some lemons it was the stylar end 
and in others the stem end which showed the higher acidity. This may 
be seen in table 1, and in the figures given in the second paragraph preceding 
this one. However, the tests, when averaged, showed practically no 
difference between the acidities of the stylar and stem ends of over 400 
normal lemons. The average of the total number of tests showed the 
stem end to be pH 0.01 more acid than the stylar end. This difference 
is so small, however, that it comes well within the limits of experimental 
error. 
Summary 
The principal results obtained by the experiments on growth rate, water 
content, and acidity of lemons at different stages of maturity may be sum¬ 
marized as follows: 
1. While the lemon tree tends toward the production of new fruits 
continuously, the age of the tree and climatic and soil conditions make the 
production more or less seasonal. In the inland districts the seasonal 
setting of new fruits is more marked than in the coastal regions. 
3 For an explanation of the term “tree-ripe” and similar terms referring to the stages 
of maturity of lemons, see the first article in this series by Bartholomew, Barrett, and 
Fawcett (1). 
