278 SPENCER MOORE [ocToBER 
have failed when it encountered a region which, except for some fresh- 
water lakes, interposed no bar to its advance. Moreover, Professor 
Tate’s generalisation is the more unsatisfactory, inasmuch as we know 
nothing about the tertiary flora of Western Australia. 
The idea that the primitive tertiary flora was an immigrant one, so 
far as concerns Australia, must therefore be regarded as exceedingly 
problematical. The wide distribution of that flora seems to show that, 
no doubt with local variations, all the countries inhabited by it enjoyed 
an approximately similar climate, and it is surely no extravagant 
hypothesis that Australia played a commensurate part with other 
countries in the evolution of the flora. Certain forms were of extra- 
Australian origin, doubtless; but we are not justified in assuming that 
one part of the great area peopled by that curious flora was shut out 
from the drama of evolution and condemned to be a passive recipient 
of forms generated elsewhere. 
The key to the problem before us seems to be in the recognition 
of the fact of there being two main elements in the Australian flora, 
one xerophilous, the other hygrophilous, and by applying the same 
classification to fossil floras, and regarding the bulk of the forms having 
a typical Australian facies as xerophilous forms; the disappearance 
from countries outside Australia of natural orders and genera now 
confined to or characteristic of it can be accounted for without assum- 
ing the possession of some natural superiority by one flora over 
another. Let us take the case of Europe, which, during Miocene and 
still more during earlier tertiary times, had a climate considerably 
warmer than it has to-day. Now if, under these circumstances, the 
country were open and included stretches of desert (and this is pre- 
cisely the character Mr. Wallace’ considers it had during the Miocene 
age), here would be conditions exactly parallel in some parts of 
Australia, particularly Queensland, to-day. And what do we find 
there? In the drier parts typical Australian species flourish, while 
species of Indo-Malayan facies predominate elsewhere. It is therefore 
probable that the species of European tertiary floras referred to 
Australian genera were, for the most part, dwellers in the desert 
patches, while the moister places were occupied, to a large extent, by 
forms adapted to the conditions there obtaining. That the climate of 
Europe gradually changed during tertiary times we know, not only 
because the floras indicate decreasing warmth until the cold Pliocene 
age arrived, but because the great upheavals during the mountain- 
making epochs must undoubtedly have affected, in a marked degree, the 
near annual temperature of the upraised districts and of the countries 
in their neighbourhood. The diminution of its temperature would 
have the effect of rendering Europe better fitted to herbaceous vegeta- 
tion ; it would, in fact, change it from what I have previously called a 
dendritic to a herbaceous zone, and thus would be set up a tendency 
1 ‘* Geog. Dict. of Animals,” vol]. i. p. 117. 
