III. INTRODUCED SPECIES. 73 



the British flora. — Sinapis arvensis and Galeopsis Tetrahit, 

 though seen most usually among corn and other crops in 

 the fields, evince much tendency to grow also on hedge- 

 banks and elsewhere. In this manner they assume a 

 second or seemingly native character, in addition to their 

 agrestal and colonist character. — Anagallis arvensis and 

 Filago germanica seem to be still more capable of main- 

 taining themselves elsewhere, apart from cultivation, and 

 ■without human aid ; although often very abundant among 

 crops, and perhaps most frequently seen on cultivated 

 ground. They are always deemed native plants ; but as 

 we pass in a northerly direction, their places of growth 

 assume more and more of an artificial character ; and at 

 length, in the Flora of Moray, where the sign of fre- 

 quency is attached to the names of both, that of doubtful 

 nativity is also added to the former. — Stellaria media and 

 Polygonum aviculare, also abundant weeds on cultivated 

 lands, are almost equally plentiful in various other situa- 

 tions ; and hence no botanist ever questions their origi- 

 nal nativity in England. —In these examj)les we trace the 

 group of colonists, from their first occasional appearance 

 as chance aliens, upwards to the undoubted natives. The 

 intervening grades or steps, between the couj)lets of plants 

 mentioned by name, might be filled up by other names, 

 in such manner as still more clearly to show that no ab- 

 solute and certain line can be drawn between them, — 

 either between the aliens and colonists, or between the 

 colonists and natives. Botanists do not agree at what 

 link or step in the series the lines of distinction can or 

 ought to be traced. True, every observer of English ve- 

 getation can recognise and admit the different conditions 

 of Stellaria media and Barkhausia setosa. So far, he 

 recognises and admits the distinctions between natives 

 and aliens. But this does not enable him satisfactorily 



VOL. IV. L 



