to the mass of vegetable matter they contain, calculated from the size as well as the number of individuals, are, perhaps, nearly equal to all the other plants of that country. They agree very generally also, though belonging to very different families, in a part of their œconomy which contributes somewhat to the peculiar character of the Australian forests, namely, in their leaves or the parts performing the functions of leaves being vertical, or presenting their margin, and not either surface, towards the stem; both surfaces having consequently the same relation to light. This œconomy, which uniformly takes place in the Acaciæ, is in them the result of the vertical dilatation of the foliaceous footstalk; while in Eucalyptus, where, though very general, it is by no means universal, it proceeds from the twisting of the footstalk of the leaf.
The plants of Terra Australis at present known, amounting to 4200, are referable, as has been already stated, to 120 natural orders; but fully half the number of species belong to eleven orders.
Of these Leguminosæ, Euphorbiaceæ, Compositæ, Orchideæ, Cyperaceæ, Gramineæ, and Filices are most extensive and very general tribes, which are not more numerous in Terra Australis than in many other countries.
Thus Leguminosæ and Compositæ, which taken together comprehend one-fourth of the whole of Dicotyledones, and Gramineæ, which alone form an equal part of Monocotyledones, bear nearly the same proportion to these primary divisions in the Australian Flora.
The four remaining orders are Myrtaceæ, Proteaceæ, Restiaceæ, and Epacrideæ. Of these Myrtaceæ, though it is likewise very general, has evidently its maximum in Terra Australis, more species having been already observed in that country than in all other parts of the world; Proteaceæ and Restiaceæ, which are nearly confined to the southern hemisphere, and appear to be most abundant in the principal parallel of New Holland, are also very numerous at the Cape of Good Hope: and Epacrideæ, at least, equally limited to the southern hemisphere, are, with very few exceptions, confined to Terra Australis.
Several other less extensive, natural families have also their maximum in this country, especially Goodenoviæ, Stylideæ, Myoporinæ, Pittosporeæ, Dilleniaceæ, Diosmeæ, and Halorageæ; but the only orders that appear to be absolutely confined to Terra Australis are Tremandreæ and Stack-
