150 MEAXS OF DISPERSAL. [Chap. XH. 



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 neisrh- 

 bouring 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 these rare wanderers 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 would be 

 the chance 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 tlie 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 simi- 

 lar means. Out of a hundred kinds of seeds or animals 

 transported to an island, even if far less well-stocked 

 than Britain, perhaps not more than one would be so 



