places are apparently occupied by the other inhabitants; in the
Galapagos Islands reptiles, and in New Zealand gigantic wingless birds,
take the place of mammals. In the plants of the Galapagos Islands, Dr.
Hooker has shown that the proportional numbers of the different orders
are very different from
what they are elsewhere. Such cases are generally accounted for by the
physical conditions of the islands; but this explanation seems to me
not a little doubtful. Facility of immigration, I believe, has been at
least as important as the nature of the conditions.
Many remarkable little facts could be given with respect to the
inhabitants of remote islands. For instance, in certain islands not
tenanted by mammals, some of the endemic plants have beautifully hooked
seeds; yet few relations are more striking than the adaptation of
hooked seeds for transportal by the wool and fur of quadrupeds. This
case presents no difficulty on my view, for a hooked seed might be
transported to an island by some other means; and the plant then
becoming slightly modified, but still retaining its hooked seeds, would
form an endemic species, having as useless an appendage as any
rudimentary organ, for instance, as the shrivelled wings under the
soldered elytra of many insular beetles. Again, islands often possess
trees or bushes belonging to orders which elsewhere include only
herbaceous species; now trees, as Alph. de Candolle has shown,
generally have, whatever the cause may be, confined ranges. Hence trees
would be little likely to reach distant oceanic islands; and an
herbaceous plant, though it would have no chance of successfully
competing in stature with a fully developed tree, when established on
an island and having to compete with herbaceous plants alone, might
readily gain an advantage by growing taller and taller and overtopping
the other plants. If so, natural selection would often tend to add to
the stature of herbaceous plants when growing on an island, to whatever
order they belonged, and thus convert them first into bushes and
ultimately into trees.
With respect to the absence of whole orders on
oceanic islands, Bory St. Vincent long ago remarked that Batrachians
(frogs, toads, newts) have never been found on any of the many islands
with which the great oceans are studded. I have taken pains to verify
this assertion, and I have found it strictly true. I have, however,
been assured that a frog exists on the mountains of the great island of
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