contended that they are perspiratory organs. This does not seem
probable from an experiment of Dr. Hales, Vegetable Statics, p.
30. He, found, by cutting off branches of trees with apples on
them and taking off the leaves, that an apple exhaled about as
much as two leaves the surfaces of which were nearly equal to the
apple; whence it would appear that apples have as good a claim to
be termed perspiratory organs as leaves. Others have believed
them excretory organs of excrementitious juices, but as the vapor
exhaled from vegetables has no taste, this idea is no more
probable than the other; add to this that in most weathers they
do not appear to perspire or exhale at all.

"The internal surface of the lungs or air-vessels in men is said
to be equal to the external surface of the whole body, or almost
fifteen square feet; on this surface the blood is exposed to the
influence of the respired air through the medium, however, of a
thin pellicle; by this exposure to the air it has its color
changed from deep red to bright scarlet, and acquires something
so necessary to the existence of life that we can live scarcely a
minute without this wonderful process.

"The analogy between the leaves of plants and the lungs or gills
of animals seems to embrace so many circumstances that we can
scarcely withhold our consent to their performing similar
offices.

"1. The great surface of leaves compared to that of the trunk
and branches of trees is such that it would seem to be an organ
well adapted for the purpose of exposing the vegetable juices to
the influence of the air; this, however, we shall see afterwards