84 The Life of the Wheat Plant from Seed to Seed. 
sent the fruit enclosing the seed. The covering proper to the 
9 seed is very delicate, and is represented by the white space be- 
tween the skin and the seed itself. The skin which represents 
the fruit or pistil (and the presence of which has led us to speak 
of the grain and not the seed) is composed of two layers, the 
10 outer being formed of larger and thicker-walled cells. Greater 
strength and elasticity is secured to the skin by the length of 
the cells of the one layer being at right angles to the length of 
the cells in the other. The swelling of the grain consequently 
does not rupture the skin. 
The food stored up in the seed for the use of the embryo, 
like that stored in the egg, is taken and used as food by man. 
The miller grinds the grain into flour. In ordinary mills the 
grain is ground between the millstones, and thereafter the skin 
or bran is separated by a series of siftings from the white flour. 
In the new roller mills the quality of the flour is greatly improved 
by the separation of the bran and the slightly coloured embryo, 
before the store of white food is converted into flour. 
The grains of wheat which contain the largest proportion of 
gluten are the most valuable for animal food. Starch alone 
cannot build up the muscle of animals. Flesh requires for its 
formation nitrogen in addition to the elements found in starch, 
and this is to be found in the gluten of wheat. Grains of wheat 
rich in gluten are translucent, and horny in section, while those 
in which it is deficient are opaque and dull white. These two 
qualities of grain have different economic values, — the one rich 
iu gluten is best for making bx’ead, the other abounding in starch 
is most valuable for malting, 
II. Germination of the Grain. 
Ji'jurex printeJ in the margin r%fer to the corresponding figures On page 93 .) 
When wheat is stored, the little plant in the seed remains 
dormant. It is not, however, free from the influence of external 
conditions. It parts with its moistm-e to the dry air, and this 
may go on till the plantlet is completely dried up and killed. 
A few years are sufficient to produce this change in a grain of 
wheat. Every well-ripened wheat seed may grow when sown 
the year after it has been harvested. But if seeds be kept for 
two years some will fail to germinate, and the number failing 
will increase year by year, till in six or eight years not a seed 
will grow. The stories of the germination of wheat that has 
been buried with mummies are only fables. The most vigorous 
and prolific crops are grown from fresh ripe seeds. 
Under the influence of warmth and moisture the plantlet 
