18 INTRODUCTION. 



the ruins of such structures as Godstow nunnery, 

 Oxfordshire, from whence I have a specimen. Such 

 historical or memorial plants have a peculiar interest, 

 and deserve to be noted, though there can be no 

 necessity for insisting, as some botanists do, that 

 they are " certainly wild," meaning thereby that 

 they had an ab origins existence in our island. There 

 can be no rational doubt that such flowers as Impa- 

 tiens fulva, and the Martagon Lily, however wild 

 they may now appear to be, or secluded the spots 

 where they grow at present, were introduced from 

 gardens. The Canadian shrub, Xylosteum tataricum, 

 Pursh, so well known by its small pink flowers, as 

 an adornment of plantations, now frequently, as I 

 have observed, gets into hedges, and spreads about 

 quite as wild as some other plants that are allowed 

 to pass muster. Species from abroad often maintain 

 themselves on ballast heaps for a time, as Linaria 

 supina, found by Mr. KEYS, at Plymouth,* and so 

 for the nonce, get reported as " true natives," until 

 again degraded, by more accurate observation, or 

 death, at the place of their appearance. But, not to 

 multiply examples that come within the experience of 

 every botanist, no one will dispute that DiantJms 

 plumarius, and D. caryopliillus, now often beautifying 

 the walls of castles, are garden derivatives ; while 

 the spread of the little Italian ivy-leaved toad- flax, 

 (Linaria Cymbalariaj) throughout England, and even 

 into remote places in Wales, is a matter of daily 

 observation. 



A remarkable circumstance in the distribution of 

 plants, particularly interesting to the botanical ob- 



* Phytologist, vol. ii. p. 39. 



