Tropical Flora.] INTRODUCTORY ESSAY. xxxix 



midity, 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, which 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, Carron, 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 Arnheim'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 Pandani (one species indicating fresh-water in the 

 interior), Br achy chiton, Adansonia, on the north-west quarter, and Cochlospermum, 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 Capparidece, Pittosporece, Bauhinia, Sterculiacea, 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 Murehison, 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 desert presents various assemblages of plants according as the soil is saline, clayey, or 

 sandy, but these plants are almost the same as those of extratropical Australia, with the exception of 

 various species of Portulacece, Solarium, Euphorbia, Cassia, Gomphrena, Ptilotus, Trianthema, Ayl- 

 meria, and other Paronychiece. 



* Report on Plants of Babbage's Expedition, (Victoria, 1858). 



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 American V. Bonariensis, and 

 I should think an introduced plant. 



