Page:Popular Science Monthly Volume 43.djvu/237

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225
ADAPTATIONS OF SEEDS AND FRUITS.

seeds which are small, pointed, and covered with hairs. The posterior end is prolonged into a hairy, corkscrew-like awn, which twists or untwists, according to the amount of moisture. This awn ends in a feather-like affair with backward-pointed hairs. On moist ground the seed-hairs stand out so as to place the seed-point downward, and the awn untwists; but the barbed feather preventing upward movement, because it catches in the herbage, the seed is forced into the soil. However, if the awn dries and contracts, the feather is easily drawn down while the seed is not drawn up. By successive moistenings and dryings the seed is ultimately driven completely into the earth.

As to vitality, seeds present widest differences. Very short-lived seeds are those of the coffee and magnolia. On the other hand, under abnormal conditions, some seeds have retained vitality for many centuries, apparently. Raspberry seeds, found in a Celtic tumulus along with coins of the Emperor Hadrian, germinated, according to good authority, after a possible interval of several centuries. Other seeds from old Roman tombs grew after a lapse of many hundred years, but these are exceptional instances. Accurate experiments show that a few kinds live for fifteen years, or thereabouts, while the majority are much shorter lived. Stories of wheat raised from seed found in mummy wrappings are founded upon no trustworthy evidence whatever.

When a forest has been removed by fire, or otherwise, it commonly happens that a fresh growth of entirely new plants immediately springs up. This may be partly due to the unusual opportunity for growth thus given to foreign seeds; but the usually accepted explanation is that the new growth is from seeds which have long lain dormant.

Finally, as regards germination, seeds accommodate themselves to surrounding conditions with considerable readiness. Some seeds are so tenacious of life as to germinate, not only when old, but also when a large share of their food substance has been destroyed, provided, of course, that the germ itself is uninjured. No seed, however, will germinate without the proper amount of moisture, free oxygen, and warmth, although other disadvantages are often withstood successfully.

We have now described some of the more evident adaptations to surroundings displayed in seeds and fruits, but by no means all; for here, as everywhere else, Nature presents a variety which is almost infinite. Although endless differences in structure are still unexplained, we must believe that they are adaptations to circumstances present or past, and our knowledge leads us confidently to expect that future discovery will reveal in increased vastness the complexity of the relations by which everything in Nature is adapted, more or less perfectly, to everything else.