Chap. XII.] MEANS OF DISPERSAL. 32& 



had found large fragments of granite and other rocks, which do not 

 occur in the archipelago. Hence we may safely infer that icebergs 

 formerly landed their rocky burthens on the shores of these mid- 

 ocean islands, and it is at least possible that they may have brought 

 thither some few seeds of northern plants. 



Considering that these 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 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 cf 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 trans- 

 port 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 ; 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 r 

 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 the last few centu- 

 ries, through occasional means of transport, immigrants from Europe 

 or any other continent, that a poorly-stocked island, though stand- 

 ing more remote from the mainland, would not receive colonists by 

 similar means. Out of a hundred kinds of seeds or animals trans- 

 ported to an island, even if far less well- stocked than Britain, per- 

 haps not more than one would be so well fitted to its new home, as- 

 to become naturalised. But this is no valid argument against what 

 wou'd be effected by occasional means of transport, during the long 



