s, some of which have
their leaves glazed by it.

The next of the vegetable materials is _fecula_; this is the general
name given to the farinaceous substance contained in all seeds, and in
some roots, as the potatoe, parsnip, &c. It is intended by nature for
the first aliment of the young vegetable; but that of one particular
grain is become a favourite and most common food of a large part of
mankind.

EMILY.

You allude, I suppose, to bread, which is made of wheat-flower?

MRS. B.

Yes. The fecula of wheat contains also another vegetable substance which
seems peculiar to that seed, or at least has not as yet been obtained
from any other. This is _gluten_, which is of a sticky, ropy, elastic
nature; and it is supposed to be owing to the viscous qualities of this
substance, that wheat-flour forms a much better paste than any other.

EMILY.

Gluten, by your description, must be very like gum?

MRS. B.

In their sticky nature they certainly have some resemblance; but gluten
is essentially different from gum in other points, and especially in its
being insoluble in water, whilst gum, you know, is extremely soluble.

The _oils_ contained in vegetables all consist of hydrogen and carbon in
various proportions. They are of two kinds, _fixed_ and _volatile_, both
of which we formerly mentioned. Do you remember in what the difference
between fixed and volatile oil consists?

EMILY.

If I recollect rightly, the former are decomposed by heat, whilst the
latter are merely volatilised by it.

MRS. B.

Very well. Fixed oil is contained only in the seeds of plants, excepting
in the olive, in which it is produced in, and expressed from, the fruit.
We have already observed that seeds contain also fecula; these two
substances, united with a little mucilage, form the white substance
contained in the seeds or kernels of plants, and is destined for the
nourishment of the young plant, to which the seed gives birth. The milk
of almonds, which is expressed from the seed of that name, is composed
of these three substances.

EMILY.

Pray, of what nature is the linseed oil which is used in painting?

MRS. B.

It is a fixed oil, obtained from the seed of flax. Nut oil, which is
frequently used for the same purpose, is expressed from walnuts.

Olive oil is that which is best adapted to culinary purposes.

CAROLINE.

And what are the oils used for burning?

MRS. B.

Animal oils most commonly; but the preference give