The Vegetation of Western Australia, i 
Iv. 
covers their broad margins. In this vegetation the Chenopodiaceae assume 
the leading role. Species of Atriplex, Bassia, and Kochia cover the ground 
with their lowly forms, relieved here and there by the more halophytic members 
of other families, which form a striking contrast in colour — the green of Hakea 
Preissii and Gasuarina lepidophloia, although the latter is green only by com- 
parison, for its branchlets are more or less glaucous. The larger shrubs are 
mainly species of Eremophila, such as E. pterocarpa and E. florihundai both 
with dense rounded crowns of light grey foliage. Only where the soil has been 
heaped into small rises do we find any relief from the drab colour scheme, and 
here we find the purple-spiked Trichinium exaltatum, stretches of pink-flowered 
PranJcenia, dense masses of halophytic Swainsona, with Senecio and Peplidiuniy 
while in the south we occasionally find dense stretches of rose-flowered Carpo- 
brotus. In the salt-pans of the mulga bush we find two halophytic Malvaceae — 
Plagianthus microphyllous and the remarkable P. Helmsii, the latter with 
a candelabra-like habit and densely packed clusters of leaves and flowers, 
looking from the distance like a Euphorbia. The hardy halophytic grasses 
are species of Eragrostis, especially E. falcata and E. lanipes, which intrude 
sparingly into the area dominated by Bassia and Atriplex. The margin of 
the surface salt, beyond which no plant life extends, is usually indicated by a 
band of the green samphires which always remain as the last rampart of the 
halophytic association. 
(e) THE TRIODIA STEPPE. 
Grass steppe occurs on the red sandy soils of the Eremean Province. It 
is most typically developed in the areas which receive a summer rainfall, 
but in a modified form it extends into the middle zone of the Eremea where the 
highest precipitations occur between March and June. It is entirely absent 
from the May-August rainfall zone except in a very impoverished condition 
near Coolgardie, to the east of Mount Holland, and near the Fraser Range, 
where the presence of Triodia tussocks in the sand-heath formation render it 
peculiar. It is, however, exactly in these marginal sand-heaths that the 
March rains are very important. 
Speaking generally, the Triodia Steppe is a formation controlled by 
summer precipitations and a sandy soil. It is the red sand that supplies 
its peculiar edaphic requirement, except in the tropical north, where it occurs 
in the stony soil of the Nullagine series, as for example the mountains and 
escarpments of the Hamersley Ranges and the Hann Plateau in Kimberley. 
The predominant genus is Triodia, comprising about a dozen species. 
This grass forms dense tussock-like masses which usually average about a 
metre in diameter, and may be cushion-like, dome-shaped, or conical. They 
are very rarely contiguous, but are separated by narrow patches of bare sand, 
and their growth continues peripherally, until in old plants the tussocks may 
be as much as four metres in diameter, ultimately tending to become annular 
as the centre dies out. Frequently, as a result of fire, these annular growths 
are interrupted, and from small nuclei, fresh tussocks are again formed, which 
in turn repeat the process. This is particularly true of Triodia Basedowii and 
T. irritans in which, in the old plants, the progressive annular development 
of the tussock results in some overlapping of the rings, causing a loose net- 
work of living culms with dead centres, or the centres may be represented 
by areas of bare red sand. The leaves of all species are pungent-pointed, 
a characteristic that renders the plants forbidding. 
The formation extends to the coast between Onslow and the Eighty-mile 
Beach, but is otherwise absent from the littoral. From the north-west coast 
