422 APPENDIX. No. V. 



the number of species collected on different parts of this line of coast, I 

 am inclined to regaixl 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 tliem, has not been correctly estimated : and that 

 the great superiority of the intratropical latio 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 tlie 

 equator to 30° lat. in the northern hemisphere at least, tile 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 higlier latitudes a gradual diminution of dicotykdones 

 takes place until in about 6'0° N., and 55° S. lat. they scarcely equal half 

 their intratropical proportion." * 



Snce 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 ptosecuted this subject 

 further, by extending the enquiry to the natural orders of plants: and in the 

 valuable dissertation prefixed to his great botanical wt)rk,-f- has adopted the 

 same equinoctial proportion of Monocotyledones to Dicotyledones as that given 



* Flinders^ Voyage to Terra AustraUs,2. p. 538. 



+ Nova Genera et Species Plantariim, quas in perigrinatione orbis novi collegerunt, 

 &c. Jmat. Boniiland et Alex, de Ilumboldt. ex sched. autogr. in rfr'd. dig. C. S. Kunlh.lSlb, 

 Parisiis. 



