the most extensive land area of the
globe where competition has been most severe and long-continued, the fact
of the existence of this power remains, and we can see how important an
agent it must be in the formation of the floras of any lands to which these
aggressive plants have been able to gain access.

But not only are these plants pre-eminently capable of holding their own in
any temperate country in the world, but they also have exceptional powers
of migration and {512} dispersal over seas and oceans. This is especially
well shown by the case of the Azores, where no less than 400 out of a total
of 478 flowering plants are identical with European species. These islands
are more than 800 miles from Europe, and, as we have already seen in
Chapter XII., there is no reason for supposing that they have ever been
more nearly connected with it than they are now, since an extension of the
European coast to the 1,000-fathom line would very little reduce the
distance. Now it is a most interesting and suggestive fact that more than
half the European genera which occur in the Australian flora occur also in
the Azores, and in several cases even the species are identical in
both.[138] The importance of such a case as this cannot be exaggerated,
because it affords a demonstration of the power of the very plants in
question to pass over wide areas of sea, some no doubt wholly through the
air, carried by storms in the same way as the European birds and insects
which annually reach the Azores, others by floating on the waters, or by a
combination of the two methods; while some may have been carried by aquatic
birds, to whose feathers many seeds have the power of attaching themselves,
and some even in the stomachs of fruit or seed eating birds. We have in
such facts as these a complete disproof of the necessity for those great
changes of sea and land which are continually appealed to by those who
think land-connection the only efficient means of accounting for the
migration of animals or plants; but at the same time we do not neglect to
make the fullest use of such moderate changes as all the evidence at our
command leads us to believe have actually occurred, and especially of the
former existence of intermediate islands, so often indicated by shoals in
the midst of the deepest oceans.

_Means by which Plants have migrated from North to South._--But if plants
can thus pass in considerable numbers and variety over wide seas and
ocean