PBIMABY DIVISIONS. 101 



Sir Joseph Banks, it appears that the species of plants col- 

 lected by Mr. Smeathman at Sierra Leone, during a residence 

 of more than two years, amounted to 450. 



On the same authority I find that the herbarium formed 

 in the neighbourhood of Cape Coast by Mr. Wilham Brass, 

 an intelligent collector, consisted of only 250 species. 



And I have some reason to believe, that the most exten- 

 sive and valuable collection ever brought from the west 

 coast of equinoctial Africa, namely, that formed by Professor 

 Afzelius, during his residence of several years at Sierra Leone, 

 does not exceed 1200 species ; although that eminent natu- 

 ralist, in the course of his researches, must have examined a 

 much greater extent of country than was seen in the expe- 

 dition to Congo. 



From these, which are the only facts I have been able to 

 meet with respecting the number of species collected [423 

 on diflFerent parts of this line of coast, I am inclined to re- 

 gard the herbarium from Congo as containing so consider- 

 able a part of the whole vegetation, that it may be employed, 

 though certainly not with complete confidence, in determin- 

 ing the proportional numbers both of the primary divisions 

 and principal natural orders of the tract examined ; espe- 

 cially as I find a remarkable coincidence between these 

 proportions 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 com- 

 parative number of species in equal areas within the tropics 

 and in the low^er latitudes beyond them, has not been cor- 

 rectly 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 



