period, as are
necessary on the view advanced by Forbes and admitted by his followers.
The nature and relative proportions of the inhabitants of oceanic
islands are likewise opposed to the belief of their former continuity of
continents. Nor does the almost universally volcanic composition of
such islands favour the admission that they are the wrecks of sunken
continents; if they had originally existed as continental mountain
ranges, some at least of the islands would have been formed, like other
mountain summits, of granite, metamorphic schists, old fossiliferous and
other rocks, instead of consisting of mere piles of volcanic matter.

I must now say a few words on what are called accidental means, but
which more properly should be called occasional means of distribution.
I shall here confine myself to plants. In botanical works, this or that
plant is often stated to be ill adapted for wide dissemination; but the
greater or less facilities for transport across the sea may be said to
be almost wholly unknown. Until I tried, with Mr. Berkeley's aid, a
few experiments, it was not even known how far seeds could resist
the injurious action of sea-water. To my surprise I found that out
of eighty-seven kinds, sixty-four germinated after an immersion of
twenty-eight days, and a few survived an immersion of 137 days. It
deserves notice that certain orders were far more injured than others:
nine Leguminosae were tried, and, with one exception, they resisted the
salt-water badly; seven species of the allied orders, Hydrophyllaceae
and Polemoniaceae, were all killed by a month's immersion. For
convenience sake I chiefly tried small seeds without the capsules or
fruit; and as all of these sank in a few days, they could not have been
floated across wide spaces of the sea, whether or not they were injured
by salt water. Afterwards I tried some larger fruits, capsules, etc.,
and some of these floated for a long time. It is well known what a
difference there is in the buoyancy of green and seasoned timber; and it
occurred to me that floods would often wash into the sea dried plants or
branches with seed-capsules or fruit attached to them. Hence I was led
to dry the stems and branches of ninety-four plants with ripe fruit, and
to place them on sea-water. The majority sank quickly, but some which,
whilst green, floated for a very short time, when dried floated much
longer; for instance, ripe hazel-nuts sank immediately, but when dried
t