ut 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 seawater; 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 blown across
the whole Atlantic Ocean, from North America to the western shores of
Ireland and England; but seeds could be transported by these wanderers
only by one means, namely, in dirt sticking to their feet, which is in
itself a rare accident. Even in this case, how small would the chance
be of a seed falling on favourable soil, and coming to maturity! But it
would be a great error to argue that because a well-stocked island,
like Great Britain, has not, as far as is known (and it would be very
difficult to prove this), received within the last few centuries,
through occasional means of transport, immigrants from Europe or any
other continent, that a poorly-stocked island, though standing more
remote from the mainland, would not receive colonists by similar means.
I do not doubt that out of twenty seeds or animals transported to an
island, even if far less well-stocked than Britain, scarcely more than
one would be so well fitted to its new home, as to become naturalised.
But this, as it seems to me, is no valid argument against what would
be effected by occasional means of transport