50 THE NATUEAL HISTORY EEYIEW. 



Carclamine liirsuta, Leonurus Sibiricus, 



Nasturtium officinale, Drosera intermedia, /3., 



Sonohus asper, J uncus tenuis, 



oleraceus, Oxalis corniculata, 



Plantago major, /3., 

 of which several are possibly introduced, and most of the rest are 

 weeds of wide dispersion. 



Whether the lofty mountains of Cuba and Haiti present a larger 

 assemblage of JSTorthern forms, we do not know ; the Mexican Alps 

 certainly do, and as there is a marked affinity between the more 

 peculiar vegetation of the Blue Mountains of Jamaica and the 

 Mexican Alps, on the one hand, and the New Grrenada ranges on the 

 other, it may prove that there has been an ancient geological con- 

 nection between these regions, previous to that cold epoch which 

 favoured the migration of Northern forms across the Tropics which 

 Mr. Darwin so plausibly advocates. Be this as it may, the almost 

 total absence of typical North American plants in the West Indies, 

 is perhaps the most singular feature in the whole Flora, one that 

 is incompatible with their having shared in the effects of a glacial 

 migration. 



On the other hand, it may be argued that the difference between 

 the temperature of the islands, and of even the warmest of the 

 North American States, is so great, that this alone may have expelled 

 what Northern plants once inhabited the islands. In favour of this 

 view, it must be stated, that it is difficult to conceive greater contrasts 

 of climate within equally small distances than obtain between the 

 Bahamas and Florida. This, as is well known, is due to the influence 

 of the Gulf stream, which, where it impinges on the American 

 Coast, does not raise its winter temperature much, but which, bathing 

 even the northernmost Bahama Islands off the Floridan coast, raises 

 their winter temperature to that of the tropics. 



As to the extent to which this induced climate may have affected 

 the Northern plants, we can only judge by observing its effects upon 

 such as have been introduced by the agency of man. Of these, a 

 small proportion ha-se run wild, or become naturalized ; and it may 

 be worth while to devote a short space to the consideration of them. 

 Fortimately Dr. Grisebach has most carefully discriminated between 

 the truly naturalized species and occasional escapes, and thus enables 

 us to extract the following information from the body of his work : — 

 In the British West Indies the naturalised species amount to less 



