284 SPENCER MOORE [ocroBER 
also only to consider the hygrophilous element in the two floras, since 
the Indo-Malayan climate is not suited to xerophilous ones. While, 
therefore, the considerable areas in Northern and North-Eastern 
Australia’ favourable to hygrophilous species have been open to the 
incursions of the whole of the rich Indo-Malayan flora, only those 
Australian forms adapted to hygrophilous have had a chance of 
penetrating into Indo-Malaya. It is submitted, therefore, that a 
preponderant migration from the north is only what ought to be 
expected on the doctrine of chances, and that there is no need to 
import into the discussion notions as to relative superiority and 
inferiority. We thus stand here upon precisely the same ground as 
that taken up in considering the supposed aggressive power of the 
Scandinavian flora. 
The case is different with the Antarctic element of the Australian 
flora. This comprises forms suited to the lower grades of temperature, 
and all available evidence teaches us that colder conditions have been, 
of course in a geological sense, temporary only in Australia. But 
bearing in mind that glacial effects must have lasted a very long time, 
as contrasted with the span of human life, we may suppose that 
species of which the ancestors were received from the south may have 
been differentiated within the wide area in Australia suited to Antarctic 
forms during glacial times and times immediately preceding and 
following them, and that some at least of such species, accompanied by 
native ones which had become adapted to colder conditions, would 
migrate south when glacial conditions passed away, and so add a new, 
if small, element of Australian origin to the Antarctic flora. In any 
event, the Antarctic element seems to be animmigrant one.” I do not 
remember any attempt to prove from the presence of Antarctic forms 
the possession of “aggressive power” by the Antarctic flora, though, 
as the evidence for migration is so much stronger in this case, the 
omission, to say the least of it, is somewhat strange. 
But Professor Tate tells us that a flora of exotic origin is in the 
act of displacing its indigenous vegetation from Central Australia. 
Let us see upon what evidence this conclusion reposes. Most of the 
truly Australian forms, he says,’ usually grow gregariously or in 
isolated colonies from a few square yards to several square miles in 
area. But in a country lke Australia, where good patches of soil 
alternate with bad ones, this gregarious habit scarcely implies want of 
adaptation. I saw precisely the same thing in Western Australia, and 
the inference I drew from it was directly contrary to Professor Tate’s, 
namely, that the large numbers of a species monopolising or almost 
monopolising considerable portions of ground argued success in their 
1 And to a somewhat more limited extent the North-West too. 
2 Some of the herbaceous genera now characteristic of northern lands represented in 
Australia may have been introduced from the south during the glacial period. 
3 ** Report of the Horn Expedition ” (Botany), p. 120. 
