In some varieties of barley the fruit is constituted of the above tissues alone and the shell, but in most the paleæ are likewise present. They consist chiefly of long fibrous, thick-walled cells, two or four rows deep, constituting a very hard layer. On tranverse section, this layer forms a coherent envelope about 35 mkm. thick; its cells when examined in longitudinal section show but a small lumen of peculiar undulated outline from secondary deposits.
The gluten-cells varying considerably in the different cereal grains, afford characters enough to distinguish them with certainty. In wheat, for instance, the gluten-cells are in a single row, in rice they form a double or single row, but its cells are transversely lengthened.
The inner tissue of the albumen in barley is filled up with large irregularly lenticular, and with extremely small globular starch granules, the first being 20 to 35 mkm., the latter 1, 2 to 3 mkm. in diameter, with no considerable number of intermediate size. The concentric layers constituting the large granules may be made conspicuous by moistening with chromic acid.
The layer alluded to as being composed of gluten-cells is loaded with extremely small granules of albuminous matters (gluten), which on addition of iodine are coloured intensely yellow. These granules, which, considering barley as an article of food, are of prominent value, are not confined to the gluten-cells, but the neighbouring starch-cells also contain a small amount of them: and in the narrow zone of denser tissue projecting from the furrow into the albumen, protein principles are equally deposited, as shown by the yellow coloration which iodine produces.
The gluten-cells, the membrane embroynnaire of Mège-Mouriès, contain also, according to the researches on bread[2701] made by this chemist (1856), Cerealin, an albuminous principle soluble in water, which causes the transformation of starch into dextrin, sugar, and lactic acid. In the husks (épiderme, épicarpe and endocarpe) of wheat, Mège-Mouriès found some volatile oil and a yellow extractive matter, to which, together with the cerealin, is due the acidity of bread made with the flour containing the bran.
Chemical Composition—Barley has been submitted to careful analyses by many chemists, more especially by Lermer.[2702] The grains contain usually 13 to 15 per cent. of water; after drying, they yield to ether 3 per cent. of fat oil, with insignificant proportions of tannic and bitter principles, residing chiefly in the husks. Lermer further found in the whole grains, 63 per cent. of starch, 7 of cellulose, 6·6 of dextrin, 2·5 of nitrogen, a small amount of lactic acid, and 2·4 of ash.
The analysis of Poggiale (1856) gave nearly the same composition, namely, water 15, oil 2·4, starch 60, cellulose 8·8, albuminous principles 10·7, ash 2·6.
The protein, or albuminous matter consists of different principles, chiefly insoluble in cold water. The soluble portion is partly coagulated on boiling, partly retained in solution: 2·5 per cent. of nitrogen, as above, would answer to about 16 per cent. of albuminous matters. Their soluble part seems to be deposited in the starch-cells, next to the gluten-cells, which latter contain the insoluble portion.
The ash, according to Lermer, contains 29 per cent. of silicic acid, 32·6 of phosphoric acid, 22·7 of potash, and only 3·7 of lime. In the opinion of Salm-Horstmar, fluorine and lithia are indispensable constituents of barley.
The fixed oil of barley, as proved in 1863 by Hanamann, is a compound of glycerin with either a mixture of palmitic and lauric acids, or less probably with a peculiar fatty acid. Beckmann’s Hordeinic Acid obtained in 1855 by distilling barley with sulphuric acid, is probably lauric acid. Lintner (1868) has shown barley to contain also a little Cholesterin ([p. 420]).