124 m. INTRODUCED SPECIES. 



all the dubiously native plants may be considered to be- 

 long to the lower region exclusively. And in some 

 instances, as intimated above, the discrepancies would be 

 very wide, in reckoning the proportions borne by the 

 several orders of systematic botany, either to each other, 

 or to the total flora of the island. 



In the first general List of species, to be printed some 

 pages forward, an intermediate course will be taken. 

 The aliens will there be omitted, and mostl}'- so in the 

 other lists to follow. But the denizens and colonists will 

 usually be retained, unless where any explanation to the 

 contrary may be given. It is easy to conceive that some 

 of the investigations, concerning the relations between 

 climate and vegetation, might be assisted by resorting to 

 the mixed flora of the island, rather than by endeavouring 

 to select one reduced as strictly as possible to its truly 

 native elements. Example. — ' Given the climate of Bri- 

 tain, — What would be the natural vegetation of the 

 island, all plants having free access to settle on it, if so 

 adapted ? ' Under this view, aU species able to establish 

 themselves fully, as Miinulus luteus and Impatiens fulva 

 have done, would be advantageously reckoned as compo- 

 nent portions of the flora. On the contrary, if it be 

 sought to trace the migrations of species, or to investi- 

 gate the past history of our insular flora, then a careful 

 elimination therefrom of every species brought into the 

 island by human agency, as Avena strigosa and Bromus 

 secalinus in all probability have been brought, becomes a 

 matter of much importance. 



This subject of introduced plants has encroached too 

 largely on the pages of the present work, and must now 

 be left for other topics. The Author has hitherto unsuc- 

 cessfully tried to induce some other botanist to write a 

 ' History of the British flora ' ; — tracing out each species 



