136 OLA I (,AI,L0K 



according to the season of the year, may transport lichen- u germs" 

 capable of germination, to Iceland, but nothing is known regarding 

 this point. At the present time it is not even possible to procure a 

 list of the lichens, which grow on cliffs inhabited by sea-fowl in 

 both Scotland and Iceland, from which an opinion could be formed 

 as to how far such transport between these countries is probable. 

 But even if there were a distinct agreement of flora between such 

 localities, that would by no means prove that the transport had 

 been made only by birds. We should be justified in assuming that 

 the lichen-"germs" have been carried along by wind or perhaps water 

 and that this agreement is due to the similarity of the substratum, 

 i. e. one especially manured by birds, as regards the solution of 

 this question, there is scarcely any other way out of the difficulty, 

 than by a direct investigation of what migrating birds can possibly 

 carry of lichen spores and parts along with them, adhering to their 

 feet or to other parts of their bodies, when they arrive at the country 

 in spring; but this will be a very minute and difficult investigation. 



But whatever the result may be at which we arrive by that 

 method, it will not be able to modify, to any degree w r orth men- 

 tioning, the view that all other means of migration taken together, 

 scarcely play so great a part in the immigration, as does transport 

 by wind. Even if we imagined all other means eliminated, the 

 flora would, in all probability, have acquired the same essential 

 composition, as that now existing, by the agency of the wind alone; 

 all our knowledge of the means of dispersal of the species is sug- 

 gestive of this. But this does not exclude the possibility that many 

 species are transported into the country in more ways than one, 

 for instance both by birds and by wind. 



It is only with regard to the few submerged species, that the 

 wind has probably played no part at all. Here I believe ocean- 

 currents, and perhaps sea-fowl, have been the transporting agencies. 



