46 H. G. SIMMONS. [SEC. ARCT. EXP. FRAM 



ted to the northern coast part? Why have they not spread southwards 

 along the coast when the same mode of conveyance might carry them 

 thither? And, moreover, why have they not gone over to the west 

 coast when the american species have reached the eastern shore ? If we 

 assume, that there has been, in post-glacial time, a land-communication 

 along which they have wandered, we get at least a somewhat better so- 

 lution of the problem, even though every point may not be settled. 

 As the way along the Arctic American Archipelago was never glaciated 

 to any considerable extent, it lay open even in early post-glacial (or late 

 glacial) time, and thus the american species got under way northwards 

 very long ago. Some may even have lived in the islands during the 

 maximum of glaciation. The eastern species had a long way over 

 which to spread, and few only reached so far as Greenland before the 

 road of migration was made impracticable by the sinking of the land. 

 Changes of climate may also have played their part in restricting these 

 pioneers to their present small area, as well as in breaking up that of 

 some of the western species in isolated parts. Such a view also agrees 

 very well with some peculiarities in the distribution of marine algae, 

 especially the Laminariaceae, which I have pointed out elsewhere 

 (SIMMONS, Relations of Floras, p. 166167). 



Now the appearance of these eastern species is, indeed, the princi- 

 pal difference between the floras of N. E. and N. W. Greenland, but it 

 must not be overvalued; the number of species common to both, is still 

 more prominent. Even if we set aside the doubtful and ubiquitous spe- 

 cies, we have left at least as many american as eastern species in the 

 flora of N. E. Greenland; and if we reckon all that have more or less 

 probably arrived from the american side, we get from four to five times 

 as many western as eastern plants. Among the three areas here com- 

 pared, that in N. E. Greenland shows the largest number of species. 

 It must, however, be kept in mind, that it begins about three degrees 

 of latitude south of the two others, and the limit of the known part of 

 the N. E. coast coincides with the southern part of the western districts. 

 This may account for the presence here of so many (1415) southern 

 species. 



North- Western Greenland shows the smallest number of species. 

 I think, however, that this is in great part due to its very imperfect 

 exploration; 15 species, found both in Ellesmereland and in N. E. Green- 

 land, are absent from the N. W. Greenland list, but probably not in fact 

 from its flora. That this about holds the middle position between those 

 of the districts on each side, appears from the different tables above; 



