ry and
physiology of vegetation, subjects on which we have yet but very
imperfect notions. Still I hope that I shall be able, in some measure,
to satisfy your curiosity. But, in order to render the subject more
intelligible, I must first make you acquainted with the various changes
which vegetables undergo, when the vital power no longer enables them to
resist the common laws of chemical attraction.

The composition of vegetables being more complicated than that of
minerals, the former more readily undergo chemical changes than the
latter: for the greater the variety of attractions, the more easily is
the equilibrium destroyed, and a new order of combinations introduced.

EMILY.

I am surprised that vegetables should be so easily susceptible of
decomposition; for the preservation of the vegetable kingdom is
certainly far more important than that of minerals.

MRS. B.

You must consider, on the other hand, how much more easily the former is
renewed than the latter. The decomposition of the vegetable takes place
only after the death of the plant, which, in the common course of
nature, happens when it has yielded fruit and seeds to propagate its
species. If, instead of thus finishing its career, each plant was to
retain its form and vegetable state, it would become an useless burden
to the earth and its inhabitants. When vegetables, therefore, cease to
be productive, they cease to live, and nature then begins her process of
decomposition, in order to resolve them into their chemical
constituents, hydrogen, carbon, and oxygen; those simple and primitive
ingredients, which she keeps in store for all her combinations.

EMILY.

But since no system of combination can be destroyed, except by the
establishment of another order of attractions, how can the decomposition
of vegetables reduce them to their simple elements?

MRS. B.

It is a very long process, during which a variety of new combinations
are successively established and successively destroyed: but, in each of
these changes, the ingredients of vegetable matter tend to unite in a
more simple order of compounds, till they are at length brought to their
elementary state, or, at least, to their most simple order of
combinations. Thus you will find that vegetables are in the end almost
entirely reduced to water and carbonic acid; the hydrogen and carbon
dividing the oxygen between them, so as to form with it these two
substances. But the variety of intermediate co