330 MEANS OF DISPERSAL. Chap. XI. 



■wliicli do not occur in the archipelago. Hence we may safely 

 infer that icebergs formerly landed their rocky burdens on the 

 shores of these niid-occau islands, and it is at least possible 

 that they may have brought thither the seeds of northern 

 plants. 



Considering that tliese 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 trans- 

 port 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 

 Avhen exposed for a great length of time to the action of sea- 

 water; nor could they be long carried in the crops or intes-« 

 tines of birds. These means, however, would suffice for occa- 

 sional transport across tracts of sea some hundred miles in 

 breadth, or from island to island, or from a continent to a 

 neighboring 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 tliey 

 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 these rare wan- 

 derers only by one means, namely, by dirt adhering to their 

 feet or beaks, which is in itself a rare accident. Even in this 

 case, how small the chance would be of a seed falling on fa- 

 vorable soil, and coming to matuiity ! 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 diffi- 

 cult to prove this), received within the last few centuries, 

 through occasional means of transport, immigrants from Eu- 

 lope or any other continent, that a poorly-storked island, 

 though standing more remote from the main-land, would not 

 receive colonists by similar means. Out of a hundred seeds 

 or animals transported to an island, even if far less well 



