V. INEQUALITIES OF DISTRIBUTION. 429 



supply numerous facts specially belonging to the botany 

 of Britain, in exemplification of the dissimilarities and 

 distinctions here mentioned. A few of such instances 

 may be cited in further explanation. 



The two longitudinal divisions of Britain, eastern and 

 western, are tracts stretching alongside of each other by 

 a wavy boundaiy line ; they are nearly equal in extent, 

 and are so narrow that no part of either can be deemed 

 far distant from some part of the other. The hills attain 

 to neaily equal heights in both ; and the extent of coast- 

 line, independently of narrow inlets or indentations of 

 the land, is much the same. These geographic uni- 

 formities, and the long line of contiguity, are very favour- 

 able to a floral identity. But even with these favouring 

 conditions, the identity is not at all complete. It has 

 been shown by the letters * w e ' in the summary of dis- 

 tribution, that several species are restricted to the 

 western division, and that several others are in turn 

 restricted to the eastern division ; the united floral diver- 

 sity amounting to fourteen per cent of the whole flora, or 

 thereabouts. 



In the three latitudinal divisions, south, middle, north, 

 the floral diversities become more numerous. It is 

 shown by the letters ' s m n ' in the summary, that each 

 of these divisions contains several species which are 

 absent from one or both of the other two divisions. The 

 floral diversity here becomes increasingly evident if 

 South Britain is compared with North Britain ; although 

 the interspace between them is not very wide. Each of 

 them produces some species which are not found in the 

 other ; the positive diversity, or added species, being 

 considerably more numerous in the southern division 

 than in the northern division. So, again, on comparing 

 the Isle of Wight and the Orkney Isles, two smaller and 



