ON BOTANICAL GEOGRAPHY. 277 



spontaneously out of their natural country, or, as you 

 call it, their habitation. 



Mrs. B. Well, then ; botanists, after having studied 

 the surface of the earth under this point of view (as far 

 as their imperfect knowledge of barbarous countries would 

 admit,) have divided the globe into twenty districts, which 

 they named botanical regions. Each of these regions 

 possesses a vegetation peculiar to itself, plants of the 

 same species being seldom found growing (naturally I 

 mean) in different regions. 



Caroline. How are these regions to be distinguished 

 from each other ? 



Mrs. B. Those whose limits are the most correctly 

 determined are separated from each other by a vast ex- 

 panse of sea. 



Caroline. Why a vast expanse ? Would not a narrow 

 sea, like the Mediterranean, serve to define the limits 

 equally well ? 



Mrs. B. No; narrow seas do not constitute a limit to 

 botanical regions. There is scarcely any difference be- 

 tween plants which grow in the north of France and those 

 growing in England, or between the plants on the two 

 opposite shores of the Mediterranean. Nor do Islands 

 in the vicinity of continents constitute a boundary, as 

 they have generally the same species of vegetation as the 

 neighboring continent ; while Islands situated at a con- 

 siderable distance from continents have often quite a dif- 

 ferent vegetation. For instance, the plants which grow 

 naturally in St. Helena and the Sandwich Isles, are al- 

 most all different from those of any of the continents. 



Emily. Then I conclude that large tracts of conti- 

 nent, also, must differ in the nature of their vegetation. 



Mrs. B. It is so in general ; but as the old and the 

 new world approach very near to each other, if they are 

 not actually united towards the north pole, the plants of 

 the northern regions are nearly the same in the three con- 

 tinents ; and the further you recede from the pole, the 

 more distinct the different regions become in regard to 

 vegetation. 



1492. Into how many Botanical Regions is the earth divided! 1493. 

 How are these regions distinguished 1 1494. What is said of seas, 

 like the Mediterranean as seeming to define these limitsl 1495. And 

 of islands; and what ones are named! 1496. What is stated of the 

 similarity in the three great northern continents, or divisions of the earth! 



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