III. INTRODUCKD SPECIES. 75 



are so situate that garden species might easily reach 

 them. Some examples may here again he selected, in 

 order to illustrate this group of doubted natives. Sem- 

 perviimm tectontm and Linaria Cymbalaria occur fre- 

 quently on roofs and wallS; but perhaps never on rocks or 

 dry banks far away from houses, unless in spots where 

 they have actually been planted or sown. Their places 

 of growth thus appearing to be alwaj^s artificial, and the 

 species certainly being often planted in such places for 

 ornament or curiosity, there seems to be strong ground 

 herein for denying their aboriginal nativity in Britain. — 

 Cheiranthus Cheiri and Antirrhinum majus occur in some- 

 what similar situations, and under very similar circum- 

 stances ; extending also occasionally to sea-cliffs, chalk- 

 pits, and other less domestic places. Though short-living 

 plants, and thus requiring to be frequently renewed from 

 seeds, they maintain their position on ruins and other 

 such artificial spots, where left undisturbed ; and in so 

 far they may be accounted more naturalised, or more 

 native-seeming, than the two former species. Still, as 

 these also have been long and much cultivated in gardens, 

 and seldom occur except in places to which they might 

 have readily spread from houses or gardens, they are pro- 

 perly suspected not to be truly wild or native species. — 

 Ornithogalum umhellatum and Galanthus nivalis appear to 

 have become thoroughly established in several jilaces ; 

 the latter especially being often seen far away from pre- 

 sent houses and gardens, along the courses of streams, in 

 coppices. See. But they have been very much cultivated 

 as ornamental plants in gardens; and the snowdrop is 

 doubtless often planted for ornament in parks and shrub- 

 beries. They increase rapidly by their bulbs, and also 

 renew by self-sown seeds ; and they are are usually very 

 tenacious in the spots where planted, or where placed by 



