422 APPENDIX. No. V. 
the number of species collected on different parts of this line of coast, I 
am inclined to regard the herbarium from Congo as containing so consi- 
derable a part of the whole vegetation, that it may be employed, though 
certainly not with complete confidence, in determining the proportional num- 
bers both of the primary divisions and principal natural orders of the tract 
examined; especially as I find a remarkable coincidence between these pro- 
portions in this herbarium and in that of Smeathman from Sierra Leone. 
I may remark here, that from the very limited extent of the collections of 
plants above enumerated, as well as from what we know of the north coast of 
New Holland, and I believe I may add of the Flora of India, it would seem 
that the comparative number of species in equal areas within the tropics and 
in the lower latitudes beyond them, has not been correctly estimated : and that 
the great superiority of the intratropical ratio given by Baron Humboldt, 
deduced probably from his own observations in America, can hardly be extended 
to other equinoctial countries. In Africa-and New Holland, at least, the 
greatest number of species in a given extent of surface does not appear to exist 
within the tropics, but nearly in the parallel of the Cape of Good Hope. 
In the sketch which I have given of the botany of New Holland, I first 
suggested the enquiry respecting the proportions of the primary divisions of 
plants, as connected with climate; and I then ventured to state that “ from the 
equator to 30° lat. in the northern hemisphere at least, the species of Dicoty- 
ledonous plants are to the Monocotyledonous .as about 5 to 1, in some cases 
considerably exceeding and in a very few, falling somewhat short of this pro- 
portion, and that in the higher latitudes a gradual diminution of dicotyledones 
takes place until in about 60° N., and 55°S. lat. they scarcely equal half 
their intratropical proportion.” * 
Since the publication of the Essay from which this quotation is taken, the 
illustrious traveller Baron Humboldt, to whom every part of botany, and espe- 
cially botanical geography, is so greatly indebted, has prosecuted this subject 
further, by extending the enquiry to the natural orders of plants: and in the 
valuable dissertation prefixed to his great botanical work,+ has adopted the 
same equincctial proportion of Monocotyledones to Dicotyledones as that given 
* Flinders’ Voyage to Terra Australis, 2. p. 538. 
+ Nova Genera et Species Plantarum, quas in perigrinatione orbis novi collegerunt, 
&ec. Amat. Bonpland et Alex. de Humboldt. ex sched. autogr. in ord. dig. C, S. Kunth.1815, 
Parisiis. 
_ 
