THE CONIFERS OF JAPAN. 479 



of the Conifers as to lead to the conclusion before expressed, that 

 Japan must for these plants be taken as a centre of dispersal. 

 That there has been a migration from the polar regions southward 

 is admitted on all sides : and that many species have been stopped 

 in their southward course by the increasing temperature, is illus- 

 trated by the distribution of the Conifers in Japan. Some species, 

 as I learn from Mr. Maries, occur in the lowlands of Tesso and 

 on the mountains of the central island, as if the climate of the 

 more southern lowlands were too hot for them, or offered such 

 advantages to other species that the Conifers were crowded out 

 by the more vigorous growth of their competitors. On the other 

 hand, tropical or subtropical types, such as Podocarpus, are not 

 able to extend far to the north. 



Not a single species is common to Europe and Eastern America. 

 If, however, we look to the genera, we find them, as has already 

 been said, with the exception of the one or two supposed endemic 

 Japanese genera, belting the globe and represented in every part 

 of the northern hemisphere. A certain number of representative 

 species have also been pointed out ; and the " representation " 

 must necessarily be closer between some species than between 

 others. This relative closeness of affinity may, in the absence of 

 more direct evidence, afford a clue to the direction in which 

 migration has taken place. Adverting, therefore, to the list of 

 representative Conifers spoken of by Dr. Gray, it will be seen 

 that the representative species of Japan and of "Western North 

 America are more closely allied than those of Japan and of 

 Eastern North America : compare, for instance, Picea ajanensis 

 and Thuyajaponica (Japan) and P. sitJcensis and T.giqantea (N.AV. 

 America). Moreover the number of representative species in 

 relation to those of Japan is greater, though only slightly so, on 

 the western than on the eastern side of the American continent. 

 The facts are too few to base safe inferences on ; but it is at least 

 a reasonable conjecture that Japan did not receive its special 

 Coniferous flora from the north, because so few of the arctic 

 species or of those from Northern Asia or Northern America are 

 found in Japan. Abies alba and the Oregon and British- Columbian 

 species, none of which occurs in Japan, are instances in point. 

 Moreover, forms which were common in the arctic regions (and, 

 indeed, in various parts of what is now temperate Europe) in the 

 Miocene epoch, and which exist now in a living state in America 

 under conditions which are not dissimilar to those which may be 



