XXXVlll. 
Charles Austix Gardner. 
Tlie same \'alue in the seasonal isoliyets of the northern wet season (the 
four conseciitive months which lie between December and April, 7.e., December- 
Mareh. or January -April), 175 mm., was found to correspond very closely with 
Avhat is considered to be the boundary of the northern sav'^annah types, and aLso 
to conform to the limits of many Indo-Malayan groups in northern Australia. 
The third climatic province is that in which the rainfall for the four con- 
secutive wettest months is less than 175 mm. It will be noticed here that 
these four months are not uniform over the area, but that the winter system 
(May-August) extends along the southern and western margin of the Province, 
as the December-March or January-April season does in the north. The 
middle zone howev'cr, experiences its four wettest months between March 
and June, exactly those months which experience the northern and southern 
maximum extensions of precipitation. The intervening months, April and 
May, have a lownr rainfall than either March (summer or northern) or June 
(southern or winter) rainfall. This seasonal incidence has, of course, a power- 
ful thermic factor which is reflected in the relative importance or absence of 
grass in the formations. Whereas the Northern Province is essentially the 
area in \vhich the Indo-Malayan Element is important, and grass the pre- 
dominant ground flora, and the Soiith-West Province the area deficient in 
grass, but in which the autochthonoxis flora holds undisputed sway, the 
characteristics of the intermediate Eremean Province correspond to an area in 
which the flora shows affinities to the regions both to the north and south,, 
admitting both to a certain extent, but liaving at the same time its own dis- 
tinctive impress, forcibly expressing the capriciousness of its climatic factor 
and preseiAung a strange duality in its herbaceous species- — -a tendency to- 
wards grass under warm influences, and dicotyledonous herbage under cooler 
conditions of moisture. 
The three climatic Provinces thus delineated are : — 
The Northern Province, the South-West Pro^dnce, and the Eremean 
Province. 
VII. THE PPOVINCES AND THEIR FORMATIONS. 
1. THE NORTHERN PROVINCE. 
The Northern Province is cliaracterised by the role whicji is played by the 
Indo-Melanesian Element, by its formations, in vhich grass takes a prominent 
part as the most important ground flora, and finally by the predominanc(^ 
of megathermic plants. Except in the riverain and mangrove formations^ 
grass occurs almost everyv'here. Sclerophyllous shrubs are in the main either 
entirely absent or very scarce, and the trees are usually sparsely distributed. 
In tlie southern dry areas Triodia steppe and Pindan occur, with savannah 
on the alluvial soils. Only where laterite is present do we find any attempt at 
a sclerophyllous formation, and these formations bear a distinctive physiognomy 
by reason of tlie frecpient occurrence of palms and broad-leaved shrubs. Even 
here the coarse grasses assume an importance which causes a sharp contrast 
with similar formations in temperate latitudes. 
It is interesting to consider briefly the role taken by the Indo-Melanesian 
plants in this Province. Apart from the mangrove formations which fringe 
the coast and become of sufficient size and density to constitute a forest in the 
estuaries, the real home of this Element is to be found in the riverain forests- 
where, under the influence of telluric water, species which are more properly 
those of the rain forest find a suitable environment independent of atmospheric 
I^recipitations. Tliis is especially true of the black muddy soils, or soils rich in 
humus. \Mu‘re the river flats are well drained, the formation ceases to exist. 
