Every seed contains a small amount of nutrition, sufficient for the sustentation of the germ of the plant, until those vessels are formed, by which the nutritive elements can be absorbed and used for the further development of the living structure.
The earth, penetrated by the sun's rays, warms the sleeping germ, and quickens it into life. For a short time the germ lives upon the seed, which, moistened and warmed by the soil, yields a kind of glutinous sap, out of which the first members of the plant are formed. And then the tender leaf, looking up to the sky, and the slender rootlet penetrating the soil, begin to draw their sustenance from the vast stores of nature.
"He causeth the grass to grow for the cattle, and herb for the service of man: that he may bring forth food out of the earth."—Psalm civ.
1151. Of what do vegetable structures consist?
Of membranes, or thin tissues, which, being variously arranged, form cells, tubes, air passages, &c. Of fibres, which form a stronger kind of membrane, and which is variously applied to the production of the organs of the plants. And of organs, formed by those elementary substances, by which the plants absorb, secrete, and grow, and fulfil the conditions of their existence.
1152. Why are seeds generally enveloped in hard cases?
Because the covering of the seed, like the shell of an egg, is designed to preserve the germ within from the influence of external agencies, until the time for development has arrived, and the conditions of germination are fulfilled.
1153. Why does a seed throw out a root, before it forms a leaf?