Tropical Flora.] INTRODUCTORY ESSAY. XXXIX 
nudity, we may assume that the tropical and temperate Australian Floras blend on both (east and 
west) meridians at between lat. 26° and 29° S.; and had we complete Floras of the included parallels 
of latitude, it would not be difficult to determine by the affinities of the peculiar (endemic) species, and 
the distribution of those that extend either north or south of those parallels v, hu h to refer to the tro- 
pical Flora and which to the temperate. 
With regard to the actual temperature of the Australian tropical vegetation, it approximates to 
the isothermal of 68°. 
The general botanical features of the tropical vegetation may be gathered from the excellent 
narratives of Leichardt, Mitchell, M'Gillivray, Canon, and especially of Mueller, for the interior, 
and of Brown, Cunningham, and M'Gillivray for the coasts. The most prominent feature is the 
rarity of Cryptogams, which are almost wholly absent in western and central tropical Australia, 
and in the islands of the Gulf of Carpentaria, but are more abundant (especially the Ferns) on 
the north-east coast. The absence of Bamboos is another very striking feature, though these are 
said to abound in Arnhcim's Land (Mueller, Linn. Journ. Bot. ii. p. 138). Epiphytic Orchids are 
also very rare. Eucalypti and Acacia form the mass of the arboreous and shrubby vegetation here as 
elsewhere throughout Australia, next to which some of the most common and noticeable arboreous 
features of vegetation are afforded by clumps of Ptmdam (one species in d ic ati n g fresh* water in the 
interior), Br achy chiton, Adansonia, on the north-west quarter, and Cochlospcrutuiu, and many other 
genera on the north-east. Casuarina, Callitris, and other large trees seem to be rare though not 
wholly wanting on the west coast. 
The principal tropical phases of vegetation described by Mueller are, — 
1 . The varied arboreous and shrubby clothing of the eastern slopes of the eastern ranges, where 
numerous Indian genera of umbrageous trees are interspersed with Australian; this, called the 
" Brushwood/' or " Cedar " country, further contains the most numerous representatives of the 
Polynesian and Malayan Floras ; together with Cycas thirty feet high, and various Palms of the 
genera Calamus, Areca, Caryota, and Livistona. 
2. The " Brigalow Scrub" extends over the elevated sandstone plains west of the coast range in 
east Australia, as far as the Newcastle range (lat. 18°-20°). This is also a very varied vegetation, 
chiefly of small trees and shrubs of Capparidem, Pittosporea, Bauhinia, Sterculiacece, etc. Here 
Delabechia and Brachychiton, form a remarkable secondary feature ; distinguished as the Bottle-tree 
Scrub, from their tumid trunks. This vegetation is elsewhere* described by Mueller as extending 
from the Burdekin to the Upper Darling rivers, and ceasing towards the south-west, somewhere near 
Mount Serle, Mount Murchison, or Cooper's river. 
3. Open downs of basalt, nearly destitute of trees, except along watercourses. The vegetation 
is chiefly herbaceous, and much of it annual ; the soil is rich, and after the rains produces a luxuriant 
crop of excellent grass and herbaceous plants.f 
4. The deserl presi uts various asa mblages of plants according as the soil is saline, clayey, or 
Bandy, but these plants are almost the same as those of < lia, with the exception of 
various species of Portulacea, Solanum, Euphorbia, Cassia, Gomphrcun, Pi i lulus, Trianthema, Ayl- 
meria, and other Paronychiea. 
* Eeport on Plants of Babbage's Expedition, (Victoria, 18 58). 
f Mueller remarks that a Verbena forms so conspicuous a feature over large tracts of country as to have sug- 
gested the name of Vervain Plains ; it is very singular that this should be the South America: 
I should think an introduced plant. 
