The Vegetation of Western Australia. 
Ixiii. 
to Meekatharra and Sandstone, in the area which receives as a rule some 
rain from the storms which visit the north-west coast. They are mostly 
of the harsh tussocky type in the dry regions, but range from the soft-textured 
species of the black soil plains to the uninviting Triodia and Plectrachne. 
The perennial grasses are dominant in the savamiah, tlie savaimah wood- 
land and the steppe. The commonest genera of the tropical savannahs are 
Themeda. Gymhopogon, Iseilema, Astrebla, several genera of the Andro- 
pogoneae, including Eulalia, Chrysopogon, Bothriochloa, and Dicanthium, 
w'hich flourish in the red loamy soils, to the many species of the Paniceae and 
the soft-leaved Triodias of the lighter soils. Sorghum stipoideum, the tallest 
of the grasses is important in Kimberley, in the monsoon woodland, and the 
sandstone savannah, extending also to the Pintlan near Broome. It attains 
a height of four metres, and frequently possesses prop-like roots from its 
lower nodes. 
An examination of the tropical genera and species discloses the fact 
that a number of these are native both to equatorial Africa and southern 
Asia, e,g., Sehima nervosum, and a nulnber of others. The number of endemic 
genera is very small. 
The grasslands reach their maximum development on the loamy soils of 
tlie northern rivers — tlie “ black-soil plains ” — alhivial areas in whicli the 
soil is rich in humus. Such areas are to be found on the Lemnard, Fitzroy, 
King Edward, and Drysdale rivers, as well as the Ord River, while there is 
an extensive area between the Prince Regent and Glenelg rivers. Further 
south, in the Fortescue-De Grey district, Eragrostis, Eriachne, Enneapogon, 
and Aristida become more important amongst the perennial species, forming 
in places large areas of open grassland on the alluvial soils. These grasses 
either occur as scattered dwarf caespitose clumps in the dry season, where, 
possessed of strong rhizomes and a dense protection of crowded outer dead 
leaves they are able to survive sustained periods of drought, or the small 
stumpy base of the plant is the only evidence of life. With suitable summer 
rains, liowever, they develop into a dense ground covering intermixed with 
shorter-lived grasses and other herbs. I have not seen this country under 
these favourable conditions, but from the impoverished residuum seen in dry 
years, and the development in the depressions locally known as “ crab-holes,” 
there can be little doubt that under conditions of adequate seasonal rains, 
these areas present a picture comparable with the South African veldt. 
The hardiest of all the grasses is Triodia, the “ spinifex ” of the interior, 
which is the most important element of the steppe, and which is also at home 
in the desert. Triodia must be regarded essentially as a psammophyte, for it 
is never seen in loamy soils, where its place is taken by Eragrostis, Eriachne, 
or Enneapogon, Not only has it a general distribution in sand throughout 
the north, but it has to a great extent overcome climatic barriers, and has 
extended as far south as Coolgardie, Mount Holland, and the Fraser Range. 
It is, however, only in the stony or sandy soils of the Nullagine series tliat 
it is n'ally at home. Few other grasses are similarly constructed to with- 
stand the climatic extremes it has to endure, and it thrives under conditions too 
dry for most other plants. The commonest speeaes of the dry steppe, it is 
also an impoi’tant constituent of the mulga bush to the e^ast and north, anel 
its prevalence or absence to a great extern! eletermines the limits of the steppe 
formation. It always occurs in large scattered tussocks, and by a peripheral 
system of stolons or rhizomes incrc'ases its girth until it ultimately extends 
