80 in. INTEODUCED SPECIES. 



localities of hedgerows and copi^ices, or plantations near 

 houses. And it is perhaps never found as a constituent 

 of the truly natural forests. It is, too, more suscei^tible 

 to frost than the former species ; apparently so in its 

 half-wild state, certainly so in most of its garden varieties. 

 These considerations suggest doubts on the aboriginal 

 nativity of the Pear-tree in England. — Prunus domestica 

 is generally allowed not to be a true wilding or native in 

 England. Prunus spinosa is fully admitted to be so ; and 

 the like remark may be extended to the intermediate 

 variety or species Prunus insititia. But the links of con- 

 nexion between them are so close and gradual, that it be- 

 comes highly difficult to show whether the Plum-tree of 

 the gardens, in all its numerous and improved varieties, 

 is truly and permanently distinct as a species from the 

 BuUace and the Sloe. So far as the Plum-tree (P. domes- 

 tica) is concerned, the question of nativity here resolves 

 itself almost into one of specific identity. — The Cherries, 

 Prunus avium and Prunus Cerasus, are now quite wild ; 

 the former much more frequent than the latter. It may 

 be, that the garden varieties are improvements of native 

 species ; or it perhaps may be, that the wild varieties are 

 the degenerated descendants of trees imported into our 

 gardens. The former view is the one most generally 

 held by English botanists. — With the single exception of 

 Ribes rubrum, in its truly wild variety R. petrcsum; the 

 several species of Eibes ought to be regarded with some 

 degree of distrust in Britain. There cannot be a doubt 

 tliat many of their alleged localities have originated from 

 seeds of their garden varieties, dispersed by man and 

 animals ; and this is true with respect to those of R. 

 rubrum, equally Avith those of other species. In the 

 mountain valleys of North England and Scotland, R. 

 rubrum appears to be truly native. But the true indige- 



