This is obvious in the
structure of the teeth and talons of the tiger; and in that of the legs and
claws of the parasite which clings to the hair on the tiger's body. But in
the beautifully plumed seed of the dandelion, and in the flattened and
fringed legs of the water-beetle, the relation seems at first confined to
the elements of air and water. Yet the advantage of the plumed seeds no
doubt stands in the closest relation to the land being already thickly
clothed with other plants; so that the seeds may be widely distributed and
fall on unoccupied ground. In the water-beetle, the structure of its legs,
so well adapted for diving, allows it to compete with other aquatic
insects, to hunt for its own prey, and to escape serving as prey to other
animals.
The store of nutriment laid up within the seeds of many plants seems at
first sight to have no sort of relation to other plants. But from the
strong growth of young plants produced from such seeds, as peas and beans,
when sown in the midst of long grass, it may be suspected that the chief
use of the nutriment in the seed is to favour the growth of the seedlings,
whilst struggling with other plants growing vigorously all around.
Look at a plant in the midst of its range! Why does it not double or
quadruple its numbers? We know that it can perfectly well withstand a
little more heat or cold, dampness or dryness, for elsewhere it ranges into
slightly hotter or colder, damper or drier districts.
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