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.
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