General observations.^ 
APPENDIX. 
587 
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 be- 
longing to very different families, in a part of their oeconomy which contri- 
butes 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 {economy, 
which uniformly takes place in the Acacias, is in them the result of the \ei- 
tical 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 Lcguminos®, Euphorbiace®, Composite, Orchide®, Cypera- 
cea 1 , G rarnine® , and Filices are most extensive and very general tribes, which 
are not more numerous in Terra Australis than in many other countries. 
Thus Leguthiinos® and Composite, which taken together compre- 
hend one-fourth of the whole of Dicotyledones, and Gramme®, which 
alone form an equal part of Monocotyledones, bear nearly the same pro- 
portion to these primary divisions in the Australian Flora. 
The four remaining orders are Myrtace®, Protcace®, Restiace®, and 
Epacride®. Of these Myrtaceae, though it is likewise very general, has evi- 
dently its maximum in Terra Australis, more species having been already 
observed in that country than in all other parts of the world; Profeacece 
and Restiacm. 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 E'pacridece, 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 
Australis are Tremandre® and Stack. 
to be absolutely confined to Terra 
