220 Prof- S)?iith's Collection of Plants in the [Sept. 



refer the origin of plants that are now dispersed in various 

 situations, Mr. Brown remarks that we may be assisted by a 

 careful examination of the geographical distribution of genera. 

 We may at least go so far as to conclude, that in doubtful cases 

 it is more probable that the plant in question should belong to 

 that country in which all the other species of the same genus 

 are found decidedly indigenous, than to that where it is the 

 only species of the genus known to exist. This mode of reason- 

 ing is applied to determine the native country of the banana, the 

 papaw, the capsicum, and tobacco, about which there had been 

 some difference of opinion among naturalists ; the result is that 

 we must refer the banana to Asia as its native climate, and the 

 other three to America. Exceptions to this general rule will, 

 however, probably be found ; the cocoa-nut, for example, there 

 is every reason to believe is indigenous in the coasts and islands 

 of equinoctial Asia, yet it is the only species of its genus which 

 does not exclusively belong to America. 



There are some valuable plants that are cultivated in most of 

 the western parts of Africa, yet were not observed in Congo ; 

 of these the most remarkable are the cocoa-nut, rice, and the 

 sweet potatoe, convolvulus batatas. 



The author observes that we have no means of determining 

 the relation which the vegetation of the eastern shores of equi- 

 noctial Africa bear to the western. The flora of Abyssinia, as 

 ascertained by Mr. Salt, has not much connexion with that of 

 Congo, and the flora of Egypt has still less. The plants of 

 Congo appear likewise to be very different from those of the 

 south of Africa, containing none of the more remarkable genera 

 and orders that are found in this district : there seems also to be 

 very little affinity between the plants of Congo and those of the 

 islands of St. Jago, or of St. Helena. There is rather more 

 affinity between the vegetables of Congo and those of Mada- 

 gascar, and the islands of France and Bourbon, and consider- 

 ably more with those of India ; while, on the contrary, they have 

 less affinity with those of equinoctial America. It is observed, 

 however, that there are several genera common to this part of Africa 

 and America that have not yet been observed in India or New 

 Holland ; and there are more than 30 species in Prof. Smith's 

 collection, which are also natives of the opposite coasts of 

 Brazil and Guiana. 



It has been questioned whether there be any species, espe- 

 cially of the dicotyledonous plants, which are found in the 

 equatorial districts both of the old and the new continent. In 

 order to elucidate this point, Mr. Brown has formed a list of 

 the plants in Professor Smith's herbarium, which are common 

 to Africa, America, and Asia; afterwards a list of those 

 that are common to Africa and America, but are not found 

 in India; and a third list of plants that are indigenous in 

 Africa and India, but not in America. The greater part of the 

 species enumerated in these lists are strictly equinoctial plants, 



