63 GENERAL REMARKS ON THE 



its Plora are Emalyphis, the Leafless Acacice and, perhaps, 

 EpacridecB, Within the tropic, at least on the East coast, 

 the departure from the Australian character is much more 

 remarkable, and an assimilation nearer to that of India than 

 of any other country takes place. Several of the pecuhar 

 orders and extensive genera of tiie principal parallel are 

 here exceedingly diminished, and none remain in nearly 

 equal proportion except Eucalyptus and the Leafless 

 Acacia. 



These two genera are not only the most widely diffused, 

 but, by far the most extensive in Terra Australis, about 

 100 species of each having been already observed ; and if 

 taken together and considered with respect to the mass of 

 587] 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 economy 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 economy, 

 which uniformly takes place in the Acacise, 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, amount- 

 ing 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 Leguminosse, Euphorbiaceee, Compositse, Or- 

 chidese, Cyperaceae, Graminese, and Filices are most exten- 

 sive and very general tribes, which are not more numerous 

 in Terra Australis than in many other countries. 



Thus Leguminosse and Compositse, which taken together 

 comprehend one fourth of the whole of Dicotyledones, and 

 Graminese, which alone form an equal part of Monocotyle- 



