14 Proceedings of the Royal Irish Academy. 



and Naias Jlexilis inhabit not only some of the western Iiish lakes, they 

 occur also in Scotland. 



If we regard these plants as ha\'ing been accidentally introduced from 

 America through the agency of wind, waves, or birds, they must have been 

 transported repeatedly to different parts of Ireland. Su- "William 'ITiiselton 

 Dyer only alludes to Eriocaidon, and seems convinced that it was brought 

 across the ocean by birds.' Messrs. Colgan and Scully do not explain the 

 presence in Ireland of these plants as being due to any such accidental 

 transport. They believe them to have reached Europe by means of an ancient 

 northern land-connexion. Mr. Praeger likewise comes to a similar conclusion 

 with regard to the origin of the American plant group in Ireland. He does 

 not favour the theory of accidental dispersal. A land surface, long since 

 destroyed, of I^-Glacial age, appeals to him as a more likely explanation of 

 the presence of the American plants.' 



The number of plants common to Europe and North America is really 

 far greater than we imagine, though very few, as we have seen, are quite 

 confined to these continents. Of those which also occur in Asia there are 

 many, like the Orchid Listcra cordata, which grows only in a few localities 

 iu the extreme east, that are apparently absent from the greater part of the 

 continent. It is probable that all these have found their way from America 

 to Europe by a direct passage. Including the horsetails and ferns with the 

 flowering plants, about 575 species are identical in Canada and Europe, and 

 only 330 in Canada and Japan or the Amur district of eastern Asia. Many 

 of these are possibly modern introductions. On the other band, we know 

 from Professor Drummond's researches that of seventy species of fossil 

 plants observed by him in the Pleistocene clays of Toronto in Canada, 

 twenty occur at the present day l>oth in that country and in Europe.' 



This seems to indicate that during the Pleistocene period, the great mass 

 of the flora common to America and Europe had already found its way from 

 the one continent to the other. Altogether our available botanical evidence 

 iu favour of a fonner land-connexion between Scotland and Labrador, by way 

 of Greenlaml and Iceland, can scarcely be considered as ver)' weighty ; yet, in 

 conjunction with the preceding factors, it acquires greater significance. 



The zoological testimony in support of this view is of a much more pro- 

 nounced character. The intei'est aroused in Ireland by the discover^' of the 

 American plants has led to research in other directions. Thus, in 1895, three 



' Drer, W. ThUellon, " Geographic*! DUiritmtion," p. 289. 



' Praeger, E. LI., " Imh Topographical Botany," p. 22. 



' DmmmoDi], A. T., " Planta common to Europe and America," p. 53. 



