NEW COLONIAL FLOEAS. 



59 



550 



569 



It would be wortb inquiring to what longitudes tbis similarity of 

 vegetation is confined within tbe tropics. We know that no such Or- 

 dinal uniformity exists between the vegetation of extratropical Africa 

 and South America, nor between that of either of these countries and 

 extratropical Australia ; and we also know that the Floras of the Me- 

 diterranean Eegion and the Southern American States, and those of 

 middle Europe and the Northern American States, differ more than 

 those of Ceylon and the West Indies in their Ordinal relations. This is 

 a most interesting subject in relation to the hypothesis of an intertro- 

 pical cold epoch, such as Mr. Darwin demands for the migration of the 

 Northern Elorato the Southern hemisphere, and which epoch, occur- 

 ring (as it must have occurred) since the creation of most of the exist- 

 ing temperate species, must have destroyed a great part of the pre-ex- 



