1899] ORIGIN OF AUSTRALIAN FLORA 285 



competition with other forms. Further, Professor Tate thinks the 

 aggressive 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 tcrrestris, Cleomc viscosa, Malvastrum spicatum, 

 Boerhaavia diffusa, Salsola kali, Mollurjo 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 tcrrestris once only, .and Salsola kali about half-a-dozen times, 

 but on only one occasion in any quantity. 1 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 enncaspirmus, 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 



1 I should 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. 



2 "Contributions to the Tertiary Flora of Australia," Mem. Geol. Surv., N. S. Wales, 

 1888. 



19 NAT. SC. VOL. XV. NO. 92. 



