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 
Ofawheatgrain: A, various integuments of the ^ reserye starch e j ther ; n 
ovary and seed, forming the husk; a, cells of 
"aleurone layer" of endosperm, loaded with the Same Cells, as in the pea 
protein grains; b, starch-bearing cells. After and bean, or the protein grains 
OBB ' 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 4070 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 constitute a very compact 
source of available nitrogen. 
Combination of food. It must not be sup- 
posed that the foods above named accumulate 
independently. On the contrary, they always 
occur associated, though one form is likely to 
be dominant. Rarely, if ever, are they so re- 
FIG. 664. Cell from en- 
dosperm of castor bean 
(Ricinus communis): p, p, 
protein grains, made up 
of amorphous proteins, crys- 
talline proteins (c) ("crys- 
talloids"), and globular 
compounds of proteins with 
calcium and magnesium, the 
globoids (g). Adapted. 
