508 X. GENERAL EEMARKS. 



these geographical groups is of greater geological anti- 

 quity than the other groups. Plighly probable as it may 

 seem to be, that existing sijecies do differ in their compa- 

 rative duration on the earth, — pei'haps vastly differ in 

 that respect, — there is still not a tittle of botanical evi- 

 dence to connect past differences of duration with present 

 differences of distribution in an}' part of Britain. 



If such a truth there be, it would prove a grand ad- 

 vance in science to find out the mode of demonstrating 

 that truth. But there is no real progress made by ha- 

 zarding idle assertions on the subject, without showing 

 the existence of credit-worthy evidence in support. And 

 something worse than no progress at all is achieved, by 

 first arbitrarily marking out spaces on a map, and next 

 pretending to illustrate them by citing false lists of spe- 

 cies in sham support ; the real distribution of several of 

 those species, ignorautly huddled together to back up a 

 pre-conceived and pre-annouuced hypothesis, being widelj^ 

 at variance with the spaces so marked on the map. (See 

 Appendix to Volume First). 



It will have become evident from the general tenor of 

 the preceding remarks, that an assignment of the various 

 species to their respective types of distribution in Britain, 

 must truly be in some measure optional or arbitrary ; that 

 is, the species of an intermediate character of distribution 

 might be assigned differently by two botanists, each acting 

 on his own individual judgment formed on the same facts. 

 No exact degree of northern latitude can be stated as a 

 limit for plants of the English type ; nor can any exact 

 degree of southern latitude be indicated for the limit of 

 plants assigned to the Scottish type. No j)recise degree 

 of eastward longitude can be specified as the limit for 

 plants of the Atlantic type ; nor can any precise degree 



