The Vegetatiox op Western Australia. 
xxxvii. 
in the rainfall, especially the seasonal rainfall. The following table illus- 
trates this diminution : — 
Station. 
Altitude. 
Distance E. 
or W. 
Rainfall 
ft. 
of escarpment. 
(points). 
Fremantle 
C 
20 
miles 
W. 
3,027 
Perth . . 
197 
10 
w. 
3,467 
Guildford 
30 
5 
> i 
w. 
3,393 
Mundaring 
975 
6 
if 
E. 
4,352 
Chidlow 
983 
10 
i! 
E. 
3,796 
Northam 
494 
40 
ii 
E. 
1,711 
Meckering 
640 
60 
a 
E. 
1,526 
Cunderdin 
733 
75 
a 
E. 
1,458 
Tammin 
800 
85 
a 
E. 
1,378 
Kellerberrin 
815 
100 
ii 
E. 
1,329 
Doodlakine 
840 
110 
a 
E. 
1,235 
Merredin 
1,042 
135 
ii 
E. 
1,292 
Walgoolan 
1,055 
155 
ii 
E. 
1,196 
Southern Cross 
1,157 
200 
i i 
E. 
1,052 
Coolgardie 
1,394 
315 
ii 
E. 
1,009 
Kalgoorlie 
1,234 
337 
ii 
E. 
951 
Rawlinna 
603 
570 
ii 
E. 
637 
Loongana 
603 
680 
ii 
E. 
615 
A corresponding diminution occurs everj"N\’here ; to the east of Geraldton, 
for example, and to the north of Esperance, the diminution takes place to a 
greater degree over a given area, and the example quoted above is the longest 
transect possible with so many stations. It is this gradual diminution that 
•accounts everywhere for the gradual changes in the vegetation, modified only 
by the edaphic factor. 
In constructing a climatic map of Western Australia which would con- 
form to the main types of vegetation, it was obvious that any consideration 
of the annual isohyets alone would be insufficient. For amongst other con- 
siderations, such rainfall statistics do not take into account the useful seasonal 
rainfall, and give no indication of seasonal periodicity, nor do they indicate 
those areas which experience a pronounced drought factor in the annual 
climatic cycle. In other words the essential elements of temperature and 
rainfall periodicity are not indicated, althougli in a very general way there 
is some correlation between the annual rainfall figures and the principal types 
•of vegetation. What is required therefore is a map embodying both pluvial 
an<l thermal factors, but this is impossible, because the temperature figures 
wei*e obtainable from 30 stations only. 
A means of employing the temperature factor was reached by considering 
the seasonal incidence of the wettest period of tlie year. At first the six 
M'ettest months were employed, but were later abandoned in favour of a season 
employing the four wettest consecutive months, and the four consecutive 
<hiest months. The isohyets obtained by a consideration of the four wet 
months, referred to throughout the tables as the '"season,” were fo\md to co- 
incide very closely with the boundaries of the three provinces of the vegetation. 
Tlie line of 175 mm. winter (May-August) rainfall is, in fact, exactly a very 
distinct line of separation, cleai’ly defining the limits of the autochthonous 
elements of the south-west, and also determining the western limits of those 
elements proper to the Eremea. It is tlie Western Australian equivalent of 
the “ Goydei' Line ” of South Australia. Apart from its significance in the 
vegetation of Western Australia, it may well prove to be a line of consideraVile 
importance in future agricultural development. 
