e valuable materials here
available, in order to ascertain how far the evidence derived from the two
organic kingdoms agrees in character; and also to obtain some general
results which may be of service in our discussion of more difficult and
more complex problems.

There are in the Azores 480 known species of flowering-plants and ferns, of
which no less than 440 are found also in Europe, Madeira, or the Canary
Islands; while forty are peculiar to the Azores, but are more or less
closely allied to European species. As botanists are no less prone than
zoologists to invoke former land-connections and continental extensions to
account for the wide dispersal of objects of their study, it will be well
to examine somewhat closely what these facts really imply.

_The Dispersal of Seeds._--The seeds of plants are liable to be dispersed
by a greater variety of agents than any other organisms, while their
tenacity of life, under varying conditions of heat and cold, drought and
moisture, is also exceptionally great. They have also an advantage, in that
the great majority of flowering plants have the sexes united in the same
individual, so that a single seed in a state fit to germinate may easily
stock a whole island. The dispersal of seeds has been studied by Sir Joseph
Hooker, Mr. Darwin, and many other writers, who have made it sufficiently
clear that they are in many cases liable to be carried enormous distances.
An immense number are specially adapted to be carried by the wind, through
the possession of down or hairs, or membranous wings or processes; while
others are so minute, and produced in such profusion, that it is difficult
to place a limit to the distance they might be carried by gales of wind or
hurricanes. Another class of somewhat heavier seeds or dry fruits are
capable of being exposed for a long time to sea-water without injury. Mr.
Darwin made many experiments on this point, and he found that many seeds,
especially of Atriplex, {258} Beta, oats, Capsicum, and the potato, grew
after 100 days' immersion, while a large number survived fifty days. But he
also found that most of them sink after a few days' immersion, and this
would certainly prevent them being floated to very great distances. It is
very possible, however, that dried branches or flower-heads containing
seeds would float longer, while it is quite certain that many tropical
seeds do float for enormous distances, as witness the double cocoa-nuts
which cro