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 plumed seeds no doubt stands in the closest relations 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 favor the growth of
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. In this case
we can clearly see that if we wish in imagination to give the plant the
power of increasing in number, we should have to give it some advantage
over its competitors, or over the animals which prey upon it. On the
confines of its geographical range, a change of constitution with
respect to climate would clearly be an advantage to our plant; but we
have reason to believe that only a few plants or animals range so far,
that they are destroyed exclusively by the rigor of the climate. Not
until we reach the extreme confines of life, in the Arctic regions or on
the borders of an utter desert, will competition cease. The land may be
extremely cold or dry, yet there will be competition between some few
species, or between the individuals of the same species, for the warmest
or dampest spots.

Hence we can see that when a plant or an animal is placed in a new
country amongst new competitors, the conditions of its life will
generally be changed in an essential manner, although the climate may be
exactly the same as in its former home. If its average numbers are to
increase in its new home, we should have to modify it in a diff