CHAP. XXIII.] ARCTIC PLANTS IN NEW ZEALAND. 



487 



don and Notothlaspi of New Zealand said to have affinities 

 with Arctic plants, while Stilbocarpa — another peculiar New 

 Zealand genus — has its nearest allies in the Himalayan and 

 Chinese Aralias. Following these are a whole host of very 

 distinct species of northern genera which may date back 

 to any part of the Tertiary period, and which occur in every 

 south temperate land. Then we have closely allied repre- 

 sentative species of European or Arctic plants ; and, lastly, 

 a number of identical species, — and these two classes are 

 probably due entirely to the action of the last great glacial 

 epoch, whose long continuance, and the repeated fluctuations 

 of climate with which it commenced and terminated, ren- 

 dered it an agent of sufficient power to have brought about this 

 result. 



Here, then, we have that constant or constantly recurrent 

 process of dispersal acting throughout long periods with varying 

 power — that " continuous current of vegetation " as it has 

 been termed, which the facts demand ; and the extraordinary 

 phenomenon of the species and genera of European and even 

 of Arctic plants being represented abundantly in South Africa, 

 Australia, and New Zealand, thus adds another to the long 

 series of phenomena which are rendered intelligible by frequent 

 alternations of warmer and colder climates in either hemisphere, 

 eulmxinating, at long intervals and in favoura.ble situations, in 

 actual glacial epochs. 



Geological changes as aiding migration.-— It will be well also to 

 notice here, that there is another aid to dispersion, dependent 

 upon the changes effected by denudation during the long periods 

 included in the duration of the species and genera of plants. 

 A considerable number of the plants of Europe of the Miocene 



plants and animals, so frequently illustrated in the present volume, removes 

 the antecedent improbability which is supposed to attach to such identifi- 

 cations. I am myself the more inclined to accept them, because, according 

 to the views here advocated, such migrations must have taken place at 

 remote as well as at recent epochs ; and the preservation of some of these 

 types in Australia while they have become extinct in Europe, is exactly 

 paralleled by numerous facts in the distribution of animals which have 

 been already referred to in Chapter XIX., and elsewhere in this volume, 

 and also repeatedly in my larger vrork. 



