Va. LONGITUDE. 44J> 



West Britain, 1305 species. East Britain, 1355 species. 

 Deducting these figures from the total flora of 1425 

 species we find the difference between the two longitu- 

 dinal floras thus : — 



Western exclusively, 70. Eastern exclusively, 120. 

 And putting the figures under another aspect, we have 

 the dissimilarities between the floras for East and West 

 Britain thus : — 



Numerical difference, 50. Floral diversity, 190. 

 And looking to the eastern and western divisions of 

 England, apart from Scotland, the floral numbers are 

 reckoned uj) from the ' census of species ' thus : — 



Scotland, 1015. W. England, 1245. E. England, 1270. 

 So that the true numerical difference between the eastern 

 and western floras of England, when the local plants of 

 Scotland are left out of count, amounts onlj' to 25 species. 

 The floral diversity is of course greater. 



In all such numerical estimates and comparisons, it is 

 constantly to be kept in recollection, that the seeming 

 preciseness given by the use of arable figures is not quite 

 real. The numerical predominance of the flora of Eng- 

 land over that of Scotland, the like predominance of the 

 flora of either longitudinal half of England over that of 

 all Scotland, and probably the slight predominance of the 

 eastern over the western flora, — each of these may be 

 held a fact or real knowledge. But the particular figures 

 given for the excess are at best only approximate and 

 variable. More exact knowledge of localities will always 

 tend to alter the numbers, one way or other, and more 

 usually in diminution of differences. The greater or less 

 aggregation of sub-species into species, or the reverse 

 process, will operate more decidedly in variation of nu- 

 merical summaries. And bej^ond these causes of change, 

 there still come in the conflicting views about nativity 



VOL. IV. S M 



