British North American Plants. 41*7 



and thence to America, can this immense gap be accounted 

 for ? Or, are we to draw the conclusion that the migration 

 was not eastward across Asia, but westward to America by 

 connecting stretches of land and by currents, existing in 

 post-pliocene and earlier times, but which subsequent geo- 

 logical changes have effaced ? Or, which I think is a more 

 reasonable hypothesis, were there not, to some extent, 

 facilities for migration in both ways, with, it may even be, 

 Canada as the country of origin of many species which 

 afterwards distributed themselves in both Asia and Europe. 

 I shall discuss these three considerations separately. 



With regard to the first consideration that, if it is con- 

 ceded that the migration of plants from Europe took place 

 across Asia, can it be explained why there is such an im- 

 mense gap in the range of numbers of these European 

 plants, it is to be observed that they are absent from 

 Alaska, from British Columbia, and from the prairies and 

 the vast wooded country to the north of them. The near 

 proximity of Alaska to Siberia, the shallow seas immedia- 

 tely surrounding the Aleutian Islands, the Kui-ile Islands 

 and the Kamtschatcan coast, and the peculiar lie of these 

 islands, all tend to convey the idea of a probable connection 

 between Asia and America in tertiary times. This con- 

 nection, a more moderate climate than now exists would 

 have made an effective highway by means of which Siberian, 

 Japanese, and American plants would have intermingled, 

 and such milder climate did exist in early tertiary times 

 there. The Japanese current — the larger branch of which 

 crosses the Pacific Ocean from Japan and skirts the Alaskan 

 and British Columbian coasts — would have also lent its aid 

 during the great lapse of time since, in carrying seeds from 

 the Asiatic to the American coast. It is, however, a singu- 

 lar fact that there are (see list already given) only eleven 

 species which in Canada are exclusively British Columbian, 

 and which at the same time are found in Japan, and that, of 

 these, nine are not only exclusively northern in British 

 Columbia, but are likewise Alaskan, whilst the other two 

 are coast forms. Two only of these eleven species, Trientalis 

 Europcea and Swertia perennis, are European. This would 



