464 Canadian Record of Science. 



in Canada, has only 21 of these represented in Europe, but 

 this is in partial keeping with the fact that in the preceding 

 Tertiary period, this order does not appear to have been 

 even known. Leguminosse — also an order of apparently no 

 antiquity — which has 14*7 species in Canada, includes in 

 these only 6 common to Europe. On the other hand, Cary- 

 ophyllacese, out of 72 species in Canada, has 23 identical 

 with European species, Naidacese out of 27 has 15, and 

 Juncacese ont of 35 has 16 identical. 



These species thus identical in Europe and America are, 

 on the evidence we have, the oldest flora still existing in 

 America. They undoubtedly existed in post-pliocene times, 

 but to account for the migration of the species from one 

 continent to another, it is necessary to have connecting 

 links of land, and, at the same time there, a suitable cli- 

 mate for the distribution of northern-temperate as well as 

 arctic and sub-arctic forms. To find a union of these two 

 conditions, it is requisite to go back to pre-glacial times 

 when a climate warmer than now existed in northern- 

 temperate and arctic America and Europe, and when the 

 relations of land and water in northern-temperate Europe, 

 and possibly arctic America, presented more favourable 

 facilities for migration. 



General Causes j oe Distribution. 



The general causes, still in force, which have affected dis- 

 tribution are well known. Eiver, lake, and ocean currents, 

 play their part in every section of the globe, not only in 

 dispersing the seeds of aquatic plants-^ but also those of land 

 species, which constantly come into connection with the 

 water. Particularly would this be the case in Canada 

 where the water communications are on such an extraordi- 

 nary scale, both on the coast line and in the interior of the 

 country. Birds form a constant source of distribution, 

 going on for ages past. That seeds and fruits are the 

 especial ftx^d of birds, that birds not only traverse great 

 distances in search of food, but large numbers of them have 

 semi-annual migrations, that the peculiar habits of birds 



