xlii. 
Ctiaiu.ks Austin Gardxkr. 
hold in the South-Wt'st because of their inability to surmount the climatic 
barriers. In any case, tlie number of genera of grasses in the South-West 
Province is exceedingly small, and the area possesses but one endemic genus, 
the monotypic Diplopogov . 
Lastly, it is the liigli degree of endemism within the Province that is one 
of its outstanding characteristics. Tliis has already been remarked upon, and 
the figure is about 80 p('r cent. L'^nlike the Northern and Eremean Provinces 
it has borrowed little or nothing except from the ancient ancestors from which 
it has evolved, and of course excepting those maritime or littoral plants whicli 
have suffered oceanic transportation, and which have obtained a foothold in 
an (mvironment whicli is not typical of the general area. 
Apart from the littoral halophytic and dune formations which require 
no particular attention beyond tlie fact they they contain more or less cos- 
mopolitan maritime, or Eremean elements, the south-western formations are 
mainly woodland and lieath types. In the extreme south-w'est, in the area 
bounded by the 500 mm. seasonal isohyet, the forest formations predominate 
except where sandy coastal plain or swamps provide unsuitable edaphic 
conditions. To the east of this area, between the seasonal isohyets of 500 mm. 
and 200 mm., the savannah woodland and heath formations predominate, while 
below the 200 mm. isohyet, sclerophyllous woodland and sand heath dominate 
the landscape. While the above isohyets may be said to determine broadly 
the limits of these formations, the edaphic factor is important in determining 
the formations under drier conditions. For example, while the edaphic factor 
is not so active in the forest areas, it does to a considerable extent determine 
the sclerophyllous woodland, savannah woodland, and heath formations, the 
sclerophyllous woodland always being determined by the soil, thus dove- 
tailing into the climatic confines. 
Formations which are more strictly edaphic are those of the swamp, the 
laterite, and the granite. It would, however, be cpiite beyond the scope of 
this essay to deal with tliese at any length, and the merest outlines must 
suffice. 
(a) THE FOREST FORMATIONS. 
(i) The Jarrah Forest. 
The distribution of Eucalyptus marginata is bounded by the 400 mm. 
seasonal isohyet, but it is only on the lateritic soils that the forest formation 
exists, for although it occuis freely on the sandy soil of the coastal plain, it 
does not in this envii'onment constitute a forest. The jarrah forest is a true 
sclerophyllous formation, remaikable for the paucity of other tree species, for 
it is not a social species, and its only associates are Eucalyptus patens and E. 
calophylla. At the same time, this is surely one of the outstanding character- 
istics of the Eucalyptus associations. These trees are rather widely branched, 
but suffer little oi‘ no ovei'lapping of their crowns, the result being a forest 
canopy easily penetrated by light. Amongst the Eucalyptus trees are smaller 
trees, mostly Myrtaceae. Proteaceae, and Casuarinaceae, e.g., Persoania, 
Eanhsia. Xylomelum^ Casuariua, and Agonis, the only one of which that 
exhibits any marked degree of plagiotropism being Banksia grandis, and to 
a lesser extent Xylomeliim occidentale. The undergrowth is composed of 
sclerophyllous slirubs from less than a metre to two or three metres high, 
pi’edominantly Mvrtaceae, Protraceae, and Leguminosae. In certain areas 
Macrozamia becomes impoitant, together with Xanthorrhoea^ while towards 
the south the remarkable suffrutescent Podocarpiis Drouyyiiana assumes im- 
portance. 
