ON THE IXFLUENCE OF PHYSIOGRAPHIC CHANGES. 31 -> 



The vegetation of the salt-bush country presents such contrasts 

 with the other Australian floi-as, and has originated through distinct 

 climatic causes, tliat it may well be studied siii gemris. I will 

 divide the Australian Endemic Flora into three types, to whichfor 

 convenience of reference I apply distincive names. (PI. XVIII.) 



1. Euronotian (lit. south-east wind) dominant in tlie south and 

 east parts of the Continent. 



2. Autochthonian (lit. of the original race) restricted to the 

 south-west corner of West Australia, and approximately coin- 

 ciding with the rain-fall limit of twenty inches. 



3. Eremian (lit. desert) dominant in the dry region, which has 

 its centre in the Lake Eyrn Basin. It corresponds with the salt- 

 bush country, and approximately coincides with the area having 

 less than ten inches of rainfall per annum. It is bounded on the 

 north and north-east by the Indo- Australian vegetation ; on the 

 east and soutli-east by the typical Euronotian Flora, and on the 

 extreme south-west by the Autochthonian. 



Tlie characteristics and peculiarities of the Euronotian and 

 Autochthonian Floras have been treated fully, as far as materials 

 were available by Sir Joseph D. Hooker in his Essay on the Aus- 

 tralian Flora, and repeated by Wallace in several of his contribu- 

 tions on the geographical disti'ibution of animals, and Sir Ferdinand 

 von Mueller has intensified the difterences between the two floras by 

 subsequent discoveries. The disemberment of the Eremian Flora 

 from the Euronotian will not materially disturb the salient 

 characteristics which separate the Euronotian from the Autoch- 

 thonian, but if we eliminate from the Autochthonian such 

 species as properly belong to the Eremian Flora, by narrowing the 

 geographic limits of the former in accordance with the botanical 

 affinities and environment we shall greatly augment the dissimi- 

 larities of the two extreme floras. 



As to where the determinating line for the Autochthonian 

 Region should be drawn, is a question of great difficulty in the 

 absence of personal knowledge of the various circumstances that 

 must be taken into consideration. Already, Sir Joseph Hooker 

 had indicated, that the -sdcinity of Shark Bay marked the blending 

 of the tropical with the Autochthonian Floras ; but I recognise in 

 the florula of Gascoigne River nothing more than an admixture 

 of subtropical forms mingled with the more prominent types of 

 the same Eremian Region, though it is certainly true that a few 

 characteristic Autochthonian species extend so far northward. 

 The plants from the ]\Iurchison River show the same general 

 facies, tliough with a larger blending of Autochthonian species, 

 as might be expected from its more southerly situation. 



On the .south coast, the Autochthonian type of vegetation 

 extends in a narrow strip certairdy to Lacapede Bay, and perhaps 

 to Cape Arid ; whilst the main mass is located in the triangle 

 formed by a line joining Doubtful Bay and Bunbury. 



