Ix INTRODUCTION, 
problems difficult of solution. As regards a very large number of northern types, 
they can be distinctly traced southward. Many exist only in isolated localities, as 
they have been driven out by climatal conditions, while others present a nearly 
continuous chain; but, speaking generally, they gradually decrease in volume from 
north to south. The theory that the Proteacee, Eucalypti, and other southern types 
inhabited Europe in early Tertiary times is far from being established on satisfactory 
data, and all the indisputable evidence points to a northward migration of these types 
and a southern origin. If it can be proved that the prototypes of Eucalyptus, 
Proteaceee, &c. existed in Europe, and that the northern outliers of these types are 
survivals of stragglers of the southward migration, it follows that differentiation equal 
to the greatest differentiation in the whole world took place in the northern hemi- 
sphere, and that there has been comparatively little beyond specific differentiation in 
the southern. This may beso, and the extraordinary development of the genera Erica, 
Mesembryanthemum, and Pelargonium in South Africa and of Ranunculus, Epilodium, 
and Veronica in New Zealand might be cited in support of the argument. 
In conclusion, a few additional remarks on the adoption of a few large primary 
regions. With regard to treating the north temperate and arctic countries as one 
primary region, it may be contended that, although there is a large number of genera 
common to Europe and western North America, to give an extreme illustration*, there is 
also a larger number not represented in the two countries, including genera numerous in 
species, such as Medicago, Cousinia, and Acantholimon on the one hand, and Dalea, Gilia, 
and Pentstemon on the other. This is true; but are the differences greater than 
between Ceylon and Borneo or between the latter and New Guinea, or between South- 
west Australia and South-east Australia? Among the numerous genera peculiar to 
West Australia are such prominent ones as Kingia, Dasypogon, Anigozanthos, Conostylis, 
Andersonia, Dryandra, Pileanthus, Verticordia, Tremandra, Platytheca, and Chorilena. 
Among those common to the two are Kucalyptus, Persoonia, Hakea, Grevillea, Dampiera, 
Leschenaultia, Myoporinee, and Xanthorrhea. Further, upwards of eighty per cent. 
of the species of vascular plants are endemic. ‘The absence of a large number of orders 
and suborders represented in Eastern Australia is also remarkable, and on a par with 
the poverty of the European Flora as contrasted with the Chino-Japanese or the North- 
American. Nevertheless few persons would refer these two areas to different primary 
botanical regions. 
* As already urged, it is a comparison of the vegetation of Eastern Asia and Eastern North America that 
reveals the most striking similarities; the affinities between these two regions being much stronger than those 
existing between the vegetation of Europe and Eastern Asia. 
t Sir Joseph Hooker sufficiently indicates in his essay on the Australian Flora the striking characteristics 
of, and the more striking diversities between, the vegetation of Eastern and Western Australia; but Dr. Engler’s 
tabular view and partial analysis of the Flora of the whole of Australia (Versuch, ii, pp. 12-54) brings out 
‘these peculiarities much more prominently. 
