This section is from "Scientific American Supplement Volumes 275, 286, 288, 299, 303, 312, 315, 324, 344 and 358". Also available from Amazon: Scientific American Reference Book.
The figure represents the longitudinal cut of a grain of wheat; it was made by taking, with the aid of the microscope and of photography, the drawing of a large quantity of fragments, which, joined together at last, produced the figure of the entire cut. These multiplied results were necessary to appreciate the insertion of the teguments and their nature in every part of the berry; in this long and difficult work I have been aided by the co-operation of Mr. Bertsch, who, as is known, has discovered a means of fixing rapidly by photography any image from the microscope. I must state, in the first place, that even in 1837 Mr. Payen studied and published the structure and the composition of a fragment of a grain of wheat; that this learned chemist, whose authority in such matters is known, perfectly described the envelopes or coverings, and indicated the presence of various immediate principles (especially of azote, fatty and mineral substances which fill up the range of contiguous cells between them and the periphery of the perisperm, to the exclusion of the gluten and the starchy granules), as well as to the mode of insertion of the granules of starch in the gluten contained in the cells, with narrow divisions from the perisperm, and in such a manner that up to the point of working indicated by the figure 1 this study was complete. However, I have been obliged to recommence it, to study the special facts bearing on the alimentary question, and I must say that all the results obtained by Mr. Bertsch, Mr. Trécul, and myself agree with those given by Mr. Payen.
No. 1 represents a superficial side of the crease.
No. 2 indicates the epidermis or cuticle. This covering is extremely light, and offers nothing remarkable; 100 lb. of wheat contain ½ lb. of it.
No. 3 indicates the epicarp. This envelope is distinguished by a double row of long and pointed vessels; it is, like the first one, very light and without action; 100 lb. of wheat contain 1 lb. of it.
No. 4 represents the endocarp, or last tegument of the berry; the sarcocarp, which should be found between the numbers 2 and 3, no longer exists, having been absorbed. The endocarp is remarkable by its row of round and regular cells, which appear in the cut like a continuous string of beads; 100 lb. of wheat contain 1½ lb. of it.
These three envelopes are colorless, light, and spongy; their elementary composition is that of straw; they are easily removed besides with the aid of damp and friction. This property has given rise to an operation called decortication, the results of which we shall examine later on from an industrial point of view. The whole of the envelopes of the berry of wheat amount to 3 lb. in 100 lb. of wheat.
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.