XXXVI. 
Charles Austin Gardner. 
by the seasonal incidence and amount of the rainfall. The thermic factor is also 
very important in distinguishing the northern from the southern rainfall 
areas, while the middle area — the Eremea— stands as a buffer between the other 
two. 
The main purpose of this thesis has been to define as clearly and as 
accurately as possible, the three vegetation provinces and to correlate them 
with the climatic provinces, for, of all the factors which determine and control 
the vegetation of the earth, the climatic factor is the most important, and 
rainfall and temperature are the most important of the climatic elements. 
The natural vegetation of a country, especially when unaffected by the 
biotic, or any other external factor, is the index of its climatic and edaphic 
factors. In Western Australia, where, in the virgin state each association 
represents an ecological climax, it is possible to learn much concerning both 
soil and climate from the study of the vegetation. In fact, it is possible to 
obtain a more or less clear picture of the climatic conditions by such a study. 
Further, there is a close correlation between the soil formations and the climatic 
types, and soil surveys in Australia are to a great extent based on the vegeta- 
tion. 
In the Introduction we discussed briefly the elements of the vegetation 
of Western Australia, showing that in the north, under conditions of summer 
rainfall and a prolonged season of drought, a type of \*egetation existed in 
which the Palaeotropic Element was at home. In the south-west, an area 
described as tlie “ triangular-crescentic area extending from Shark Bay to 
Israelite Bay ” came under the influence of the autochthonous element, 
largely made up of the Antarctic and Australian Elements. It is the region 
which comes under the active influence of the winter rains, with a summer 
period of drought. The third area, which we call the Eremean Province, is 
an intermediate area characterised by a capricious climate, of uncertain 
regularity, of extreme temperatures, and dependent upon the rainfall systems 
of the neighbouring provinces for what rain it receives. This area we found 
to be dominated by the Neo-Australian Element, which is derived from botli 
southern and northern sources of origin. 
The boundary of the South-West Province can be determined within 
comparatively narrow limits, allowing for certain edaphic variations, and is 
primarily determined by the gradual diminution of the winter rainfall, partly 
by teniperature, and to a great extent by the seasonal variability of the rain- 
fall. 
As we pass from the coast towards the interior we notice a cliange in 
the formations, from high forest, through v'oodland and heath to mulga- 
bush and ultimately steppe and desert. Ihit quite apart from these changes, 
there is a graduation in the floristic composition. As we approach the bound- 
ary of the South-West Province we notice that the autochthonous species 
become gradually more rare, first we are aware that such plants as Anigo- 
zanthos and Conostylis gradually disappear, and in turn the Epacridaceae 
cease. Gradually we find an increase in the species of Eremophila, of certain 
Chenopodiaceae, and in the woodland the Zygophyllaceae and Compositae 
become increasingly important, together with a more open formation of the 
woodland ground flora. The actual line of the boundary can be determined 
by the ephedra-like species of Eremophila, Zygophyllum, and Chenopodiaceae, 
while in the heath formations we find the last of the south-west elements 
in Boronia and Epacridaceae. These, and some other indicative elements 
announce that we are passing from the South-West to the Eremea. Quite 
apart from changes in the soil, this is brought about by the gradual diminution 
