218 Prof. Smith's Collection of Plants in the [Sept. 



primary divisions of plants ; secondly, to notice whatever appears 

 most remarkable in the several nataral orders of which the col- 

 lection consists ; and thirdly, to compare the vegetation on the 

 line of the river Zaire with that of other equinoctial countries. 



The number of species in the herbarium somewhat exceeds 

 600 ; and although many of them are imperfect, yet they may 

 all be referred to their primary division, and most of them to 

 their natural families. With respect to the proportionate num- 

 bers of the three divisions, the dicotyledonous plants amount to 

 460, the monocotyledonous to 113, and the acotyledonous, 

 including the ferns, to 33 species only. Mr. Brown observes, 

 that it is important to ascertain whether a collection of plants 

 that was made in two months, and not at a very favourable 

 season of the year, can afford us sufficient data for forming any 

 conclusion respecting the proportional numbers of the three 

 primary divisions, or of the principal natural orders belonging to 

 the country in which it was collected. In order to form a 

 judgment in this respect, he compares the collection of Smith 

 with those of other naturalists who have explored the neigh- 

 bouring parts of the African coasts, or parts lying in similar 

 latitudes, particularly that of Adanson, formed on the banks of 

 the Senegal, those of Smeaton and Afzelius, procured from 

 Sierra Leone, and that of Brass, collected near Cape Coast. 

 The result of this comparison is very favourable to the value of 

 the present herbarium ; so that Mr. Brown concludes that it 

 forms so considerable a part of the whole vegetation, as to enable 

 us to determine with tolerable confidence the proportional num- 

 bers both of the primary divisions, and of the principal natural 

 orders of the tract examined. Mr. Brown remarks that from the 

 information which we at present possess, it would appear that 

 the comparative number of species in equal areas within the 

 tropics, and in the lower latitudes beyond them, has not been 

 correctly estimated. Humboldt's observations on the American 

 intertropical regions seem to prove that the western continent 

 differs in this respect from the eastern ; in Africa and New Hol- 

 land, the richest districts would appear to be not those between 

 the tropics, but about the latitude of the Cape of Good Hope. 



In his essay on the botany of New Holland, Mr. Brown first 

 pointed out the connexion between the climate of a country and 

 the proportion of its primary divisions of plants ; he particularly 

 noticed the proportion between the dicotyledonous and monoco- 

 tyledonous plants, which from the equator to about 30° N. is 

 nearly as five to one ; while beyond these limits there is a gra- 

 dual diminution of the former, until at about 60° N. and 55° S. 

 latitude, " they scarcely equal half their intertropical proportion." 

 The observations of Humboldt lead to the same conclusion 

 respecting the proportions of the primary divisions of the intertro- 

 pical plants But although this may be established as the 

 general rule, it would appear that there are many deviation* 



