Because they are encased in a hard covering upon which the gastric juice of animals takes no effect. This provision has been made by the Creator, for the preservation of seeds, the productions of which are so essential to animal life.
The gastric juice can dissolve any other part of the plant, even the woody fibre, and yet upon the seed it takes no effect. When, however, the seed is crushed, and, thereby, the vital principle destroyed, so that no plant can spring from it, the gastric juice acts upon it, and it is soon dissolved.
Hence graminivorous birds are provided with gizzards to break the protecting coats of the grain; and animals that feed on seeds and nuts strip them of their shells and husks.
It is remarkable that in the succulent fruits, such as the strawberry, the raspberry, currant, apple, orange, melon, &c., and which, from their very nature, are likely to attract animals to use them, and in eating which the seeds are likely to be swallowed, they are fortified by a doubly-protective coating; the pips of the apple, orange, &c., and the seeds of the strawberry and raspberry, pass through the digestive organs, not only unharmed, but their germinating powers are even improved by the warmth and trituration of the stomach. Indeed, the stomachs of quadrupeds and birds have been made the vehicles of propagating plants, and distributing them to the widest geographical latitudes. It is even said of some seeds that they will not germinate until they have passed through the digestive organs of an animal.
"And it was commanded them that they should not hurt the grass of the earth, neither any green thing, neither any tree."—Revelation ix.
1287. Why do animals that graze, crop the tender blades of grass, but avoid the tall stems?
Because they are tempted by the greater sweetness and tenderness of the young blades; and in this temptation a very important end is served; for, by avoiding the stems that have grown up, the animals spare the matured plant by which seeds are borne, and by which the supply of food is to be continued.
1288. Why do the eggs of butterflies lie dormant during the winter?