ON THE INFLUENCE OF PIIYSIOCRAPIIIC CHANGES. 317 



particular T liave selected for illustration the Morula of the 

 depressed country surrounding Lake Eyre, within which the 

 conditions are the most unfavourable to maintain life. 



The following table gives the number of species in each botanical class, 

 and the number of those which are endemic and extra Australasian : — 



E-^^-- AusS^sian. Total. 



Exogens 263 ... 42 ... 30o 



Endogens 42 ... 16 ... 58 



Vascular cryptogams ... ... 5 ... 5 



305 63 36S 



All the extra- Australasian species belong to the Oriental 

 Province, and the majority of them inhabit the sandstone table- 

 lands of the Western Peninsula of India, and even to Northern 

 Baluchistan, where the climate becomes dry for a considerable 

 portion of the year, This type of the Oriental vegetation is 

 largely interspersed throughout the tropical tracts of the Eremian 

 Region, and imparts a facies which is absent in the tropical portions 

 of the Euronotian Region where lowland and maritime types of 

 the Indo- Malay Sub-Province predominate. 



As I am not yet prepared to analyse the whole Eremian floras, 

 I will substitute in its stead that of the Extratropical South 

 Australian portion, with which I have some personal acquaintance, 

 and which I believe to be fairly representative of the entire flora. 



Within this region, diversity of soil exercises a great influence 

 on the botanical physiognomy, particularly as regards the perennial 

 constituents of the flora, and taken in conjunction with their 

 gregarious habits originates a high degree of monotony. Indeed, 

 the vegetation is sharply defined into that of the hills, and on rock 

 formations, that on the sandhills, that on the clay-plains and dry 

 beds of water-courses. 



The total number of species catalogued for that portion of the 

 Eremian Region within Extra-tropical South Australia is 813, of 

 these -170 are peculiar, and 343 extra limital, but of the latter 

 46 are essentially Eremian, so that more than half the species are 

 limited to this region. Of the extra-limital species, 137 are 

 extra- Australasian, 108 of which are Oriental, and the remainder 

 are Pahvarctic, Andean, or cosmopolitan types. There remains 

 206 endemic species which are common to this region and neigh- 

 bouring ones, 80 of them are migi-ants from the tropical parts of 

 the Euronotian Region, but the bulk of the remainder have 

 immigrated from the temperate parts of the same region ; whilst 

 with the Autochthonian Region the interchanges do not exceed 

 seven. 



A brief survey of the Eremian Flora as a whole in respect to its 

 ordinal and generic features, oflers, as regards the first, no very 

 positive characters, if we except Zygophyllete, Ficoidete, Salsolacea?, 



