Vn. LONGITUDE. 



451 



from any special adaptation to the eastern or western 

 climate, or to such a geographical position ? 



Likely enough this question might be answered affirm- 

 atively, if we were enabled to ascertain the origin of these 

 species in their present localities, or should try the expe- 

 riment of naturalising them on the other side of the island. 

 Cotoneaster vulgaris and Potentilla rupestris are established 

 and reputed native in single localities in North Wales. 

 Draba aizoides and Dianthus ccesius occur in single coim- 

 ties farther southward on the same western side of Britain. 

 AU four will thus find place in any list of species exclu- 

 sively western. And yet it seems difficult to point out 

 any peculiarity in the technical or j)hysiological charac- 

 ters of these four plants, in their climatal requirements, 

 or in their distribution on the continent of Europe, which 

 wiU account for their exclusively western abode in Britain. 

 On the contrary, antecedent expectation might have 

 deemed them equally or even more likely to occur in the 

 eastern provinces. Perhaps the ruj)estral character of 

 their localities, or else the qualities of the rocks on which 

 they grow, may be the nearest explanation towards ac- 

 counting for the western restriction of these four plants 

 in Britain ; and this may be so, whether they ought to be 

 held native or naturalised there. Under this view, their 

 exclusively western position may be considered a geo- 

 gi-aphical accident, connected with strictly topogi-aphical 

 circumstances, and not with longitude. 



In direct counterpoise to those four western species, an 

 equal number of others may be cited as found only on the 

 eastern side of England, although antecedent expectation 

 might have placed them on the western side instead ; 

 namely, Frankenia Icevis, Dianthus prolifer, Isuardia pa- 

 lustris, Digitaria humifusa. These four eastern-English 

 species are less local than the four western-English 



