chap, xxiii.] ARCTIC PLANTS IN NEW ZEALAND. 
487 
don and Nototlilaspi 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, 
culminating, at long intervals and in favourable 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 work. 
