which constitute the greater
part of all plants, also the acids which are found in sour fruits, etc.
Various as are all of these things in their characters, they are
entirely composed of the same ingredients (carbon, hydrogen and oxygen),
and usually combined in about the _same proportion_. There may be a
slight difference in the composition of their _ashes_, but the organic
part is much the same in every case, so much so, that they can often be
artificially changed from one to the other.

As an instance of this, it may be recollected by those who attended the
Fair of the American Institute, in 1834, that Prof. Mapes exhibited
samples of excellent sugar made from the juice of the cornstalk, starch,
linen, and woody fibre.

The ease with which these proximates may be changed from one to the
other is their most important agricultural feature, and should be
clearly understood before proceeding farther. It is one of the
fundamental principles on which the growth of both vegetables depends.

The proximates of the first class constitute usually the greater part of
all plants, and they are readily formed from the carbonic acid and water
which in nature are so plentifully supplied.

[Why are those of the second class particularly important to
farmers?

What is the general name under which they are known?

What is the protein of wheat called?

Why is flour containing much gluten preferred by bakers?

Can protein be formed without nitrogen?

If plants were allowed to complete their growth without a supply of this
ingredient, what would be the result?]

The _second class_ of proximates, though forming only a small part of
the plant, are of the greatest importance to the farmer, being the ones
from which _animal muscle_[H] is made. They consist, as will be
recollected, of carbon, hydrogen, oxygen and _nitrogen_, or of _all_ of
the organic elements of plants. They are all of much the same character,
though each kind of plant has its peculiar form of this substance, which
is known under the general name of _protein_.

The protein of wheat is called _gluten_--that of Indian corn is
_zein_--that of beans and peas is _legumin_. In other plants the protein
substances are _vegetable albumen_, _casein_, etc.

Gluten absorbs large quantities of water, which causes it to swell to a
great size, and become full of holes. Flour which contains much gluten,
makes light, porous bread, and is preferred by bakers, because it
absorbs s