I.IC.HENOLOGY OF ICELAND 135 



species it occurs, but if it be found in about 20 species, that is no 

 doubt all, and does not form even one-tenth of the species. The 

 chief means of propagation of crustaceous lichens is, as we know, 

 ascopores. 



In the foliaceous lichens it has been found in the species 

 about 9 mentioned above, that is to say, in about one-sixth of 

 the total number of species. 



In how many species of fructicose lichens it has been found, 

 cannot be stated with any certainty, but doubtless, the number does 

 not greatly exceed that of the foliaceous species. 



Whether any immigration has taken place by means of de- 

 tached portions of thallus which have been conveyed by the 

 wind, it is impossible to decide. It has been mentioned above that 

 this mode of dispersal plays a considerable part within the boundaries 

 of the country, with regard to many of the fruticose and foliaceous 

 lichens. But whether portions of thallus, capable of germination, are 

 really transported through the air from the surrounding countries, 

 cannot, of course, be known, but the possibility is scarcely pre- 

 cluded. 



Judging from the above, the role which we must assume that 

 the wind has played in the immigration and emigration of Iceland's 

 species, is thus very considerable, as all the crustaceous lichens and 

 the majority perhaps even all - - of the fructicose and foliaceous 

 lichens have such means of dispersal (ascospores, pycnocodia, soredia 

 and detached pieces of thallus) as justify us in believing that the 

 wind in particular has transported them to the country. 



Water has played a far less considerable part as a means of 

 dispersal, in fact, it can be assumed only with regard to the few 

 submerged Verrncaria spp., and the emergent V. manra, that they 

 have immigrated by this means. They occur doubtless, over nearly 

 the whole of the Arctic, and over great parts of the adjoining climate- 

 areas, on cliffs out in the sea. They are common on the coasts of 

 Greenland, Iceland, Norway, the Fseroes, Denmark and Great Bri- 

 tain, consequently both in Arctic and in temperate regions. They 

 constitute altogether not above 2 3 % of the flora of Iceland. 



What importance animals have had as regards immigration 

 is quite unknown. Here again it must suffice us to frame questions 

 which will, perhaps, in the future, be taken up and answered by others. 



Primarily it may be supposed that birds of passage which 

 migrate backwards and forwards between Iceland and milder regions, 



