The sap is changed into a viscid fluid, which circulates under the bark:
this is called _cambium_. When it is too abundant it is effused, part of
its water evaporates, and it becomes gum. If the vital circle is not
interrupted, the fluid traverses the branches, and the peduncle arrives
in the ovary, and constitutes the pericarp. In this passage it is partly
modified: it appropriates to itself the oxygen of its water of
composition; hence the malic, citric, and tartaric acids. As the fruit
becomes developed, the pellicle thins, becomes transparent, and allows
both light and heat to exercise a more marked influence. It is during
this period that maturation commences. The acids react on the cambium,
which flows into the fruit, and, aided by the increased temperature,
convert it into saccharine matter; at the same time they disappear,
being saturated with gelatine, when maturation is complete.--_London
Medical and Surgical Journal_.
We may here observe that in a recent paper, by Mr. J. Williams, in the
Transactions of the Horticultural Society, the cause of apples becoming
_russet_ is attributed to the alternating temperature, light, shade,
dryness, and moisture, which occur many times in the course of a day,
when July or August is showery. Continued rain, preceded and followed by
a cloudy sky, does not seem to produce the same effect, but the sudden,
intense light which commonly succeeds a shower at the time the fruit is
wet, injures the skin, and occasions small cracks, like the network upon
a melon.
* * * * *