The Vegetation of Western Australia. 
XXI. 
A list of the gi'oups which comprise the Indo-Melanesian Element would 
be beyond the scope of this treatise. It is sufficient to state that it includes 
the Palaeotropic Rhizophoraceae, many Leguminosae and Gramineae, Santa- 
laceae, Lauraceae, Menispermaceae, Ulmaceae, Moraceae, Burseraeeae, Melia- 
ceae, Euphorbiaceae, Anacardiaceae, Celastraceae, Sapindaceae, Rhamnaceae, 
Malvaceae, Tiliaceae, many of the Parietales, Myrtiflorae-Myrtoideae, the 
Primulales, and a host of tropical Sympetalae. 
While we postulate a land connection for the greater number of plants 
comprising the Palaeotropic Element, it must be remembered that a number 
have undergone an oceanic migration. Such plants as the Rhizophoraceae, 
Terminalia, Carapa, Thespesia, Barringtonia, and Camptostemon being ex- 
amples, as well as the maritime Spinifex and certain dune species. They 
remain principally as littoral plants. 
In addition to those groups or species which we regard as belonging 
essentially to the Palaeotropic Element, there are several groups which, while 
perhaps or palaeotropic origin, have become so modified, or have undergone 
such an extensive development, that they are no longer recognisable as typical 
examples. Indeed, in some instances they have assumed such importance in 
Australia that they have been regarded by some authors as typifying the 
Australian Element. I propose to consider, by way of illustration, one Order, 
tlie Leguminosae. 
In the first family of this Order is the genus Acacia, This genus, whicli 
is represented in the tropics of both the east and west hemispheres, com- 
prises over 500 species, of which 400 are indigenous to Australia. Of the 
six Sections, four are represented in Australia (all being in Western Aus- 
tralia), the remaining two being found in America, Africa, and Asia. The 
most primitive form of Acacia is that which possesses compound leaves. 
Acacia Farnesiana, which may be regarded as an archetype, inhabits the 
tropics of both the old and new worlds, extending from America, through 
Africa, Arabia, and India, into northern Australia. In Western Australia it 
extends as far south as the Murchison River, while in eastern Australia it 
occurs as far south as the interior of New South Wales. Within the high 
summer rainfall areas, e.g., in Kimberley, it is of fairly general distribution 
as a shrub of the savannahs, but south of the Fitzroy River it is confined to 
the alluvial soil of watercourses and depressions. 
The remaining species of the Section Gumniferae in Australia are all 
endemic and of tropical distribution as far as Western Australia is concerned. 
Acacia Farnesiana alone of the Bipinnatae connects the tropical species of 
this genus with the temperate Bipinnatae in south-w'estern Australia. Acacia 
pulchella, the most widespread of the latter, extends northwards to the south- 
ern limits of Acacia Farnesiana and southwards to the forest areas where it 
connects with the remainder of the species of its Section, the Pulchellae, which 
number twelve, and are of considerable importance in the high rainfall forest 
area of the south-west. Apart therefore, from a northern gi’oup consisting 
of the Gumniferae and the single representative of the Botryocephalae (A, 
pachyphloia), and a southern group in which there are 12 species of the Pul- 
chellae, the two being connected by the riverain A, Farnesiana, there are no 
other leafy Acacias in Western Australia. In eastern Australia a similar 
development may be noted, Acacia Farnesiana continuing the line of de- 
velopment into New South Wales, while a south-eastern group (Botryocephalae) 
extends from the north to Victoria and South Australia. 
