vpon Native Vegetables. 63 



not a little of this difference in the number of species depends 

 upon the fact, that the neighbourhood of great towns has been 

 better explored than situations remote from the ordinary scenes 

 of botanical research ; while another part of the difference may 

 arise from species not planted by the hand of Nature, having, 

 from various causes, found a footing in the vicinity of towns. 

 Considering the obvious result from the rudiments of a parti- 

 cular species not having had access to a certain spot, we ought 

 not hastily to conclude, that the absence of a particular plant 

 arises from the station being unfavourable to it. Thus, when 

 we reflect upon the progress frequently made in the neighbour- 

 hood of gardens by plants which are not natives, it must be ap- 

 parent that a certain region may be sufficiently congenial to 

 various species never planted in it by the hand of Nature. It 

 should likewise be recollected, that it is sometimes possible to 

 detect, even in a limited space, a difference of vegetation with- 

 out any appreciable alteration in the rock, soil, elevation, or ex- 

 posure ; on which account, when we meet with an example 

 wherein two neighbouring rocks of different natures are clothed 

 each with a vegetation differing from that which is found upon 

 the other, we ought not to attribute this circumstance without 

 hesitation to the dissimilarity of the rocks. Indeed it may be 

 suspected that the apparently accidental circumstances which 

 regulate the dispersion of seeds are, much more than the condi- 

 tion of the rocks, concerned with the manner in which plants 

 are arranged. 



Viewing, in connection, all the preceding facts and considera- 

 tions, it must be impossible to maintain, that with respect to 

 the great bulk of vegetables, particular species belong exclusively 

 to particular rocks. The opinion has nothing to render it a 

 priori probable, nor is it supported by any facts worthy of at- 

 tention ; whereas the view which it has been here attempted to 

 establish, accords well both with reasoning and experience. It 

 has appeared that the mass of vegetables common in a portion 

 of the north of Scotland, are equally abundant in a southern 

 part of the kingdom, and no less so in a district of France. 

 The species, no doubt, increase in these two latter situations ; 

 but that circumstance, as already mentioned, ought to be im- 

 puted to con.siderations distinct from the rocks, particularly to 



