INTROBUCTORY EXPLANATIONS. 13 



merated, within which aiiy locaUties are recorded for the 

 species. But in that work these index-Usts ai'e of coiu'se 

 limited to the " rarer plants ;" the localities of which formed 

 the object of the Guide. Here, on the contrarj^, the pur- 

 pose is different ; and it becomes necessary to show the 

 area and census of every species, whether rare or common, 

 bj a fonnula which shall apply to all alike. 



How is tliis to be accomplished ? To enumerate in piint 

 all the coimties for each species in succession, would prove 

 a very lengthy and expensive method. And if this were 

 done, the multitude of county -names, constantly to be re- 

 jieated mider the more widely distributed species, might 

 rather confuse than assist the ideas of those botanists who 

 wished to ascertain their areas. At best, too, the number 

 of counties would be exceedingly inexact, tlu-ough the want 

 of coimty-hsts of the commoner species : some of the more 

 common might even be made to appear the less common 

 species, through that deficiency. 



The comities being thus too nmnerous, while the tlu'ee 

 ancient political divisions (England, .Wales, Scotland) ai'e 

 too few and miequal for the objects of this work, an inter- 

 mediate set of sections became uecessaiy, — lai'ger than 

 counties, smaller than kingdoms. In fixing upon such in- 

 termediate sections, it has appeai'ed most convenient to 

 make them in conformity with the old established diAdsions 

 into kingdoms and comities ; as much regard being still 

 given to the physical geography of Britaui, as is consistent 

 with the prescribed rule. In forming these sections, a me- 

 sial line was first traced fi'om the south coast of England, 

 northwards into the Highlands of Scotland ; the fine cor- 

 responding with the boimdai'ies of coimties, and being- 

 traced in that comse wluch would best divide the coimties 

 whose rivers flow to the east coast, fiom those whose waters 



