364 
GEOGRAPHICAL DISTRIBUTION^, 
Chap. XI. 
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 hun¬ 
dred 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 favour¬ 
able 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 
