CH. XIV] PALAEOBOTANICAL STANDPOINT 147 



appear to have been greater destruction in America than in 

 East Asia. Such a conchision is not wholly unexpected, and mav 

 help to suggest in part the fate of some of the older species. " 



In travelling to and fro in latitude in America, the plants 

 would find themselves mostly in a country of great plains; not 

 so in East Asia, where successions of north and south mountain 

 chams existed in those old times, as in the present. It is known 

 that many of the chmatic changes which occurred during the 

 Pleistocene were fairly rapid. When such rapid changes happen 

 m a flat country, it may result that a migrating flora may be 

 overtaken in its travel by the change of climate, and in that 

 case many of its components will be exterminated, whereas in 

 a mountain country, by change of altitude, they may escape. 



Such facts may in part account for the lesser survival of 

 Pliocene species in America than in East Asia. If so, it would 

 seem that in part extinction in America too was due to killincr 

 out, ^ 



Age and Area. Let us now turn to the main theme of the 

 subject and inquire whether the Chinese-North- American flora 

 has any evidence to offer as to present distribution in connection 

 with age. Taking it as a whole, we see an ancient flora associated, 

 either fossil or living, with the widest possible range in longitude. 

 Is there any evidence that it shows wide distribution in latitude 

 associated with age? Such distribution would appear to me, 

 certainly in the case of a flora Avith a dispersal originating in 

 polar regions, to be a far more crucial test of age than dispe*-sal 

 in longitude, for with a circumpolar flora as a source of dispersal, 

 with a cooling climate, spread would be equatorwards through 

 all possible regions. The distance of travel would therefore be 

 measured, not by span in direction of longitude, but by travel 

 in latitude. In the case of the Chinese-North-American flora 

 there is some evidence that travel in latitude is an accompani- 

 ment of age. It is too small to be estimated quantitatively, but 

 is seen in the presence, especially among the older Pliocene 

 floras (Reuverian and Pont-de-Gail), of such genera as Hakea, 

 Symplocos, Styrax, Pulanisia, and Trichomnthes, which have a 

 present distribution into the southern hemisphere. The evidence 

 as to the source and direction of migration of the Chinese-North- 

 American flora to which they seem to belong indicates that these 

 genera too are migrants from the north, and that their present 

 distribution in latitude is partly due to age. 



10—2 



