446 X. GENEEAI, REMARKS. 



localities, one on each side of a provincial boundary line, 

 might be held equally local with another species found in 

 two distinct localities within the same single province. 

 For example, Myosotis alpestris is an extremely local 

 jjlant in England ; but it is placed both in the eastern 

 and western floras, in the provinces of Humber and 

 Lakes, because its one locality is stated to be crossed by 

 the provincial boundary line. And through this pecu- 

 liarity, the plant is decejitively made to appear more 

 frequent in England than in Scotland, if the census is 

 taken by provinces or sub-provinces, or even counties, as 

 shown on pages 267, 309, 335. 



7. Relation of Plants to Longitude. 



In the higher latitudes of the northern hemisphere 

 various plants- may be said to surround the globe with 

 zones of the same species, diffused more or less con- 

 tinuously amid the general mass of vegetation ; but their 

 localities not widely dissevered anywhere, except by the 

 oceans which intervene between the old and the new con- 

 tinents. Everywhere, intermingled with such widely- 

 spread plants, others aJ.so occur which are more restricted 

 in their diffusion, and which successively displace one 

 another, or are substituted one for the other ; thus con- 

 stituting different combinations of species, or native 

 floras, in every country and considerable space of 

 surface. 



In the warmer latitudes, and in the austral heniisj)here, 

 the floras present less of the specific identity, more of the 

 substitutions, under different longitudes. But with those 

 distant lands and dissimilar floras this present treatise 

 has no concern. To understand the flora and vegetation 

 of Britain, it is not necessary to pass many degrees far- 



