ds from one
part to another of the arctic and antarctic regions, as suggested by Lyell;
and during the Glacial period from one part of the now temperate regions to
another. In the Azores, from the large number of the species of plants
common to Europe, in comparison with the plants of other oceanic islands
nearer to the mainland, and (as remarked by Mr. H. C. Watson) from the
somewhat northern character of the flora in comparison with the latitude, I
suspected that these islands had been partly stocked by ice-borne seeds,
during the Glacial epoch. At my request Sir C. Lyell wrote to M. Hartung to
inquire whether he had observed erratic boulders on these islands, and he
answered that he had found large fragments of granite and other rocks,
which do not occur in the archipelago. Hence we may safely infer that
icebergs formerly landed their rocky burthens on the shores of these
mid-ocean islands, and it is at least possible that they may have brought
thither the seeds of northern plants.

Considering that the several above means of transport, and that several
other means, which without {364} doubt remain to be discovered, have been
in action year after year, for centuries and tens of thousands of years, it
would I think be a marvellous fact if many plants had not thus become
widely transported. These means of transport are sometimes called
accidental, but this is not strictly correct: the currents of the sea are
not accidental, nor is the direction of prevalent gales of wind. It should
be observed that scarcely any means of transport would carry seeds for very
great distances; for seeds do not retain their vitality when exposed for a
great length of time to the action of sea-water; nor could they be long
carried in the crops or intestines of birds. These means, however, would
suffice for occasional transport across tracts of sea some hundred miles in
breadth, or from island to island, or from a continent to a neighbouring
island, but not from one distant continent to another. The floras of
distant continents would not by such means become mingled in any great
degree; but would remain as distinct as we now see them to be. The
currents, from their course, would never bring seeds from North America to
Britain, though they might and do bring seeds from the West Indies to our
western shores, where, if not killed by so long an immersion in salt-water,
they could not endure our climate. Almost every year, one or two land-birds
are