ons; and during the Glacial period from one part of the
now temperate regions to another. In the Azores, from the large number
of plants common to Europe, in comparison with the species on the other
islands of the Atlantic, which stand nearer to the mainland, and (as
remarked by Mr. H.C. Watson) from their somewhat northern character, 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 burdens 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 these several means of transport, and that other means,
which without doubt remain to be discovered, have been in action year
after year for 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;
but would remain as distinct as they now are. 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 their very long immersion in salt
water, they could not endure our climate. Almost every year, one or two
land-birds are blown across the whole Atlantic Ocean, from North
America to the western shores of Ireland and England; but seeds could be
transported by