140 AGE AND AREA FROM A [pt. ii 



those needed for the northern invasion must have occurred, 

 possibly at intermediate periods. 



Such are the problems which present themselves for solution 

 when we attempt to apply the results of the comparative study 

 of Pliocene and Pleistocene floras to the postulated migrations 

 of the New Zealand flora. Whether the geology of New Zealand 

 and Indo-Malaya will bear out the possibility of these changes 

 of sea-level associated with the corresponding changes of climate, 

 it is for students of those regions to say. The answer is outside 

 the range of my knowledge. 



Extermination. The study of West European Phocene floras 

 led to the recognition of an extinct Tertiary flora in West Europe. 

 This flora, which I have named the Chinese-North-American 

 Association of Plants, is now represented by two living plant 

 associations; the one the forest-belt flora of the East Asian 

 mountains, the other the allied flora of parts of North America. 

 There is much evidence from recent and fossil botany, and 

 geology, to show that all three are migrant floras, branches of a 

 common polar or circumpolar flora, which migrated southward 

 in later Tertiary time under the influence of a cooling climate in 

 the Northern Hemisphere. The travel southward of each branch 

 must have extended over manj^ himdreds, more probably thou- 

 sands, of miles. In the end there resulted the complete exter- 

 mination of the European branch, and the isolation of the other 

 two, in regions of the Old and New World rcspecti\xly, separated 

 by many thousand miles of sea and land. 



In the history of this flora we see exemplified two kinds of 

 extermination, both of which are concerned with the questions 

 raised by the study of Age and Area. In the first place we have 

 regional extermination; no trace being left, in the region where 

 such extermination occurs, of the life that has been. In the 

 second place we have specific extermination; the species being 

 killed, but an alhed one taking its place. 



Regional Extermination. Regional extermination, as 

 illustrated by the history of the Chinese-North-Ameriean flora, 

 may be of different degrees. 



(1) It may be confined to o?2.£r region only. We have numerous 

 instances of this in our flora. Take, for example, the genera 

 Magnolia, Liriodendron, Menispermum, and Nyssa. These have 

 been exterminated in Europe, but have survived in East Asia 

 and North America ; though they are now represented by different 



