No. 5 indicates the testa or episperm. This external tegument of the berry
is closer than the preceding ones; it contains in the very small cells
two coloring matters, the one of a palish yellow, the other of an orange
yellow, and according as the one or the other matter predominates, the
wheat is of a more or less intense yellow color; hence come all the
varieties of wheat known in commerce as white, reddish, or red wheats.
Under this tegument is found a very thin, colorless membrane, which, with
the testa or episperm, forms two per cent. of the weight of the wheat.
No. 6 indicates the embryous membrane, which is only an expansion of the
germ or embryo No. 10. This membrane is seen purposely removed from its
contiguous parts, so as to render more visible its form and insertions.
Under this tissue is found with the Nos. 7, 8, and 9, the endosperm or
perisperm, containing the gluten and the starch; soluble and insoluble
albuminoids, that is to say, the flour.
The endosperm and the embryous membrane are the most interesting parts of
the berry; the first is one of the depots of the plastic aliments, the
second contains agents capable of dissolving these aliments during the
germination, of determining their absorption in the digestive organs of
animals, and of producing in the dough a decomposition strong enough to
make dark bread. We shall proceed to examine separately these two parts of
the berry.