in. INTRODUCED SPECIES. 77 



England, botanists are unfortunately too ready to report 

 them equally as natives in many other places, where they 

 certainly are not so. — Polemonium cc^rulenm and Meco- 

 iiopsis camhrlca, while equally traceable back to gardens 

 in many of their present localities, are quite admitted to 

 be genuinely native in some others of them ; being there 

 the occupants of wild rocky places, to which they are 

 most unlikely ever to have been transported from gardens. 

 When brought from such native spots into gardens, they 

 seed very freely, and rapidly propagate themselves in a 

 ■weed-like manner ; occasionally passing thence into adja- 

 cent wilds, where they may become mistaken for native 

 plants. — Here, again, as in the case of corn-field weeds, 

 we might trace all gradations from the certainly intro- 

 duced species, like Sempervivum and Cymbalaria, up to 

 certainly native species, the areas and separate localities 

 of which have been largely increased by human agency, 

 as in the case of the Meconopsis and Polemonium. But 

 the like difficulty again comes in our way ; namely, how 

 to designate many of the intermediate plants, which are 

 supposed natives by botanists A, B, C, and are considered 

 as introduced species by botanists D, E, F. 



3. American species. — Among the plants now seen wild 

 and well-established in Britain, are some few which can 

 be most confidently placed in the category of aliens. 

 Such are the species which were apparently unknown in 

 Europe before the discovery of America, which are cer- 

 tainly natives of the Western Continent, and concerning 

 which there is evidence, more or less positive, of an intro- 

 duction into Europe by human agency, whether purposely 

 or accidentally. In Britain we now see a few of these 

 species rapidly naturalising themselves among the natural 

 vegetation of the island. Already some of them are so 

 completely established, as a constituent portion of the 



