XV11 



labiate proceed from South America ; why so large a pro- 

 portion of the Passion-flowers are natives of the New World, 

 and nearly all the Roses of the Old. The exceptions indeed 

 which occur to the generality of these observations do but 

 enhance our perplexity. Had the whole of one family been 

 circumscribed within certain geographical limits, it might 

 have been surmised that there was some yet undiscovered con- 

 dition of climate, which had determined their distribution ; 

 but when we find plants of similar structure indigenous in 

 continents so disconnected from the one which harbours 

 the greater number of species, it becomes difficult to believe 

 that climate can have anything to do with the matter. 



The same inference seems to follow from the fact, that 

 where a single species of a genus occurs on one continent, 

 its representative, although not the same species, often 

 exists in corresponding latitudes on the other. Thus two 

 Plane-trees, the one from the eastern, the other from the 

 western hemisphere, flourish side by side on the lawns and 

 in the parks of Great Britain; and thus throughout the 

 world we find only three herbaceous species of Panax, four 

 or five of Stillingia, and three Planeras, in all which cases 

 it is remarkable that one species inhabits the Eastern, the 

 others the Western World, or vice versa. 



b 



