1899] ORIGIN OF AUSTRALIAN FLORA 285 
competition with other forms. Further, Professor Tate thinks the 
ageressive nature of alien plants to be exhibited not only by their 
extensive distribution, but by their ability to adapt themselves to 
extremes of soil and climate. He cites the following species in 
illustration: Tribulus terrestris, Cleome viscosa, Malvastrum spicatum, 
Boerhaavia diffusa, Salsola kali, Mollugo hirta, and Pollichia zeylanica. 
Now, even granting these to be aliens, and I think there are grave 
reasons for doubting the exotism of more than one of them, if these 
alien migrants from a hygrophilous zone are better adapted to desert 
conditions than native species which have had the advantage of long 
adaptation, it is strange that their distribution in the desert should be 
so restricted. Only four of the seven have been recorded from the 
western desert at all. I myself met with but two of them, viz. 
Tribulus terrestris once only, and Salsola kali about half-a-dozen times, 
but on only one occasion in any quantity.’ Moreover, it should be 
remembered that these are all herbs of wide extra-Australian dis- 
tribution, and provided, most of them, with special means of diffusion. 
Their presence in the desert is, therefore, easily explicable, and there 
is no warrant for drawing, as an upholder of current notions might 
wish to draw, from the fact any inference as to the superiority of an 
exotic flora over the native flora as a whole. On the gorges of the 
tablelands and on the basal part of the craggy escarpments and their 
taluses Professor Tate found a mixed flora in which the endemic 
element predominated, ten per cent only of it being of (supposed) 
exotic origin. The exotic species are seven in number; of these, 
except Hybanthus enneaspirmus, reported only from Mount Squires, on 
the eastern border of the western colony, Parietaria debilis alone has 
been found in the western desert. And when we compare the two 
lists above-mentioned, a curious fact comes out, namely, that the name 
of not one species occurs in both, and this forces one to suspect that 
Professor Tate has overestimated the adaptability of these supposed 
alien species. It would be wise, therefore, to reserve judgment on so 
difficult a point as that mooted by Professor Tate. 
The view here taken up, it will be observed, is one intermediate 
between that of writers who, basing their conclusions on present 
distribution alone, profess to trace “currents” of vegetation from one 
part of the world to another, and ascribe the moving force, if the term 
may be allowed, of these currents to some natural inferiority of forms 
native to the country towards which the current is supposed to set— 
between this view and that of Baron von Ettingshausen,? who, while 
? Tshould have been only too happy to come across Salsola kali more frequently, as it is 
an excellent fodder for camels. Doubtless it is much more common in South Australia, for on 
the occasion referred to above, our Afghan, who had worked at camel establishments in the 
eastern colony, at once recognised the plant, calling it ‘‘ South Australian salt-bush,” and 
informing me that it is an important fodder-plant there. 
* “Contributions to the Tertiary Flora of Australia,” Mem. Geol. Surv., N. S. Wales, 
1888. 
19—wnar. sc.—voL. xv. No. 92. 
