. A textbook of botany for colleges and universities ... Botany. 392 PHYSIOLOGY. of wheat is apparently a part of the network of protoplasm in which the starch grains are imbedded. The best known storage forms appear in vacu- oles of the endosperm in seeds. The proteins accumulate in the small vacuoles, and upon the loss of water, characteristic of maturation for a resting period, become more and more con- centrated, until finally they solidify,' forming the " aleu- rone'' or protein grains. These Fig. 663.—Outer portion of a cross section are very commonly associated of a wheatgrain:;.,v
. A textbook of botany for colleges and universities ... Botany. 392 PHYSIOLOGY. of wheat is apparently a part of the network of protoplasm in which the starch grains are imbedded. The best known storage forms appear in vacu- oles of the endosperm in seeds. The proteins accumulate in the small vacuoles, and upon the loss of water, characteristic of maturation for a resting period, become more and more con- centrated, until finally they solidify,' forming the " aleu- rone'' or protein grains. These Fig. 663.—Outer portion of a cross section are very commonly associated of a wheatgrain:;.,variou. integuments of the ^j^j^ ^^^^^ ^^^^^j^ ^ithg^ in ovary ana seed, forming the husk; o, cells of ' ** aleurone layer" of endosperm, loaded with the Same celis, as m the pea protein grains; 6, starch-bearing cells. —After and bean, or the protein grains are characteristic of certain cells, as in wheat and other cereals, where they abound in the outer layer of the endosperm (fig. 663). In large grains some proteins may crystallize out, as in the castor bean (fig. 664) and the Brazil nut, but oftener they remain apparently homogeneous. Amides. ^ Amides occur in such quantities, especially in some sappy reservoirs, that they may be considered as stored food. There they may form 40—70 per cent of the nitroge- nous materials. Alkaloids.—Some recent studies of cacao ("cocoa ") and coffee make it probable that their alkaloids (see p. 415), which are of a different type from most, may be a form of surplus nitrogenous food, since they come again into use. They constituie a very, compact source of available nitrogen. Combination of food. — It must not be sup- posed that the foods above named accumulate independentiy. On the contrary, they always occur associated, though one form is likely to be dominant. Rarely, if ever, are they so re-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability
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