162 THE VEGETABLE WORLD. 
Fleshy fruit is green in the first phase of its development. It 
then, like all the green parts of vegetables, gives out oxygen 
during the day, and carbonic acid in the night. But its bulk 
soon increases, and it receives through its peduncle the moisture 
and other substances indispensable to its growth. During this 
first period, the principles immediately soluble take their rise, and 
their proportions increase as the fruit is developed. These soluble 
bodies are—tannin, the organic acids, which vary with the fruits, 
malic, citric, or tartaric acid preponderating in some; sugar, gum, 
and pectine in others. The formation of pectine, the substance 
from which the jel/y of our household delicacies is prepared, is the 
result of a sort of reaction of the acids on a substance insoluble in 
water, alcohol, and ether: a substance which almost always 
accompanies the cellulose in the tissue of vegetables. 
Sugar proceeds from the modification of certain neutral matters, 
such as gum and starch. In fact, starch exists in large quantities 
in some green fruits, but it completely disappears at the time of 
ripening. It is extremely probable, therefore, that it is the starch 
which is transformed into sugar (glycose) under the influence of 
acids. Tannin itself, existing in almost all green fruit, is not 
found in the mature state, but seems also to be changed into 
. glycose under the influence of acids. 
The absence of acidity in fruit is the most curious fact attending 
its maturity. It has been stated that this disappearance is not 
owing to the saturation of acids with mineral bases, that the acids 
are not hidden by the sugar or mucilaginous matter existing in 
the ripe fruit, but that they are really destroyed during the ripen- 
ing process. Tannin disappears first, and then the acids. 
The moment when the tannin and acids have disappeared is 
that in which the fruit is most delicious; in a short time the sugaT 
itself disappears, and the fruit becomes insipid. About the period 
of maturity, fruits exhale carbonic acid. They no longer disen- 
gage oxygen during the day; they breathe, so to speak, after the 
manner of animals. 
Fruit at last undergoes a third modification ; it becomes mellow. 
This new change has the effect of expelling from the fruit certain 
principles which belong to it. A Medlar, for example, at first 
very acid and astringent, loses its acid and tannin, and becomes 
