XX. 
Charles Austin Gardner. 
the development in South Africa is even greater than in Australia, and there 
are again no conjunctive genera. In all cases in the Proteaceae, where a 
genus exists in South-Western Australia, it is more powerfully developed 
there than elsewhere. 
At the same time, there are several genera common to both Australia 
and South Africa, some of which will be discussed under the Palaeotropic 
Element, but the following are genera confined to the countries mentioned : — 
Chrysithrix 
Tetraria 
Wurmhaea 
Biilbine 
Caesia 
Podocoma 
Trichocline 
South Africa and S.W. Australia. 
.... South Africa and S.W. Australia. 
.... South Africa and S.W. Australia. 
.... South Africa and temperate Australia. 
South Africa and temperate Australia. 
.... Australia and America. 
.... S.W. Australia and S. America. 
These are but a few examples of the Antarctic Element, and when floral 
statistics have been completed for Western Australia, further additions will 
probably be made. Sufficient evidence has, however, been advanced to 
indicate the close relationships which exifet between certain southern groups. 
2. THE PALAEOTROPIC ELEMENT. 
The Indo-Melanesian Element is expressed by those plants which are 
common to Australia, Indo-Malaya, and Melanesia. In Australia they are 
most in evidence along the Northern Australian littoral, especially in the 
high rainfall districts of Queensland, and extending through the rain-forest 
into New South Wales. The Element is also fairly well indicated in Western 
Australia in the Kimberley district, especially in the littoral, the riverain 
forest, and the monsoon woodland. The conditions governing its migration 
are the requirements of a megathermic flora, and, while it is most strongly 
represented in Western Australia in the Kimberley district, it has migrated 
fairly extensively along the littoral tracts. This must have taken place 
at a time ■when the climatic conditions were very different from those of to-day. 
The Element has not only strongly established itself in Kimberley, but its 
residuals may be found fairly well represented to-day in the De Grey River 
district, and the Hamersley plateau. At one time it extended as far south as 
the South-West, for it has not only imdoubtedly exerted an influence on the 
flora of the South-West, there are today certain representatives of this Ele- 
ment as far south as the karri forest. There can, indeed, be no other ex- 
planation for the occurrence of such plants as Cartonema, Dioscorea, and 
Clematocissus in regions between Geraldton and Perth. At the same time, such 
a direct line of commmiication would explain certain northern migrations of 
plants that are typically southern, e.g., Byhlis, certain Droserae and Jacksonia, 
to the tropics. Finally, if further evidence is wanted, one has but to consider 
the flora of the Pilbarra district — the region between the De Grey and Ash- 
burton rivers — ^which is today an ‘‘island” supporting the impoverished 
I'esiduals of the Indo-Melanesian Element under conditions which are generally 
imsuitable, either as lithophytes or species of the declivities. Examples such 
as Livistona, Astrotriclia, Owenia, and several herbaceous species, also the 
few endemics, such as Elachnanthera, as megathermic plants of mesophytic 
or hygrophytic derivation, are evidence of a former pluvial area which must 
have been of importance in bridging the line of communication between the 
north and south. 
