Distribution of Genera.'] 



INTRODUCTORY ESSAY. 



genera belong to the same Natural Orders, and in many cases to peculiarly Australian Orders or 

 divisions of Orders. 



I have endeavoured to estimate this difference by tabulating the genera and species of each 

 country, and though the results must, in the present state of our knowledge, be very vague, they may 

 serve to give an approximate idea of the amount of difference, which it is all the more important to 

 do because I believe the phenomenon to be without a parallel in the geography of plants. These 

 Floras I estimate as containing about — 



The South-eastern Flora, including Tasmania. 

 Natural Orders .... 125 

 Genera . . . . ' . . 700 

 3,000 



South-western. 

 Natural Orders .... 90 



Genera 600 



Species 3,600 



As far as I can make out, about one-fifth of the south-eastern species are found beyond that 

 area ; but only one-tenth of them are found in south-western Australia. 



I need not remind my readers that these countries are in the same parallel of latitude, are not 

 remarkably different in physical conditions, or indeed by any means so different as others (Greece 

 and Spain for example) that present no such contrast, and that the extreme distance between them is 

 only 1 700 miles, with continuous land throughout. What differences there are in conditions would, 

 judging from analogy with other countries, favour the idea that south-eastern Australia, from its 

 far greater area, many large rivers, extensive tracts of mountainous country and humid forests, would 

 present much the most extensive Flora, of which only the drier types could extend into south-western 

 Australia. But such is not the case altogether, for though the far greater area is much the best 

 explored, presents more varied conditions, and is tenanted by a larger number of Natural Orders 

 and genera, these contain fewer species by several hundreds. 



Of the largest genera of south-eastern and south-western Australia there are very few species 

 common to both countries, as the following list, arranged in order of their magnitude, will show.* 



Si'i'tli-castern A est ralia. 



Acacia . . . 



Grevillea . . . 



Eucalyptus . . . 



Pultenaea . . . 



Leucopogon 50 



Persoonia . . . 



Eurybia . . . 



Pimelea . . . 



Epacris . . . 

 Prostanthera 



Goodenia . . . 



Hakea . . . 



Borouia . . . 



pecies. 



Sp. found in S.W. 





133 







Melaleuca 



67 







Helickrysum 



55 







Brachycome 



50 







Xerotes 



50 







Prasopbylluin 



40 







Pterostylis . 



36' 



1 



Senecio 



35 



1 



Hibbertia 



34 







Phebaliuin . 



30 







Bossiaaa 



30 







Cares 



28 



1 



Ozothanmus 



27 







Pleurandra . 



pecies. Sp. found in S.TV. 

 27 



25 3 



24 4 



24 



* This list is very far from complete, but is in so far founded on exact data as that I have satisfied myself 

 of the whole number of species alluded to in the first column of figures being absent in the collections I have 

 examined from south-west Australia, except when otherwise stated. Future observations will no doubt modify its 

 details without vitiating the general result. 



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