GEOGRAPHICAL DISTRIBUTION 327 



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 

 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, wherej 

 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 

 (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 



