398 THE NATIONALITY OF PLANTS. 
not stated that it grows on any places but on roofs and walls. 
Why should not Sedum album, S. dasyphyllum, and S. reflexum, 
Saxifraga tridactylites and Holosteum umbellatum, be all united 
under one category, whatever that may be, instead of forming 
nearly as many distinct classes as there are plants? We ave 
never seen these plants except on artificial erections; we have 
never heard of their being collected except from some artificial 
habitat or artificial aeration of soil. Sedum album has been 
reported from rocks at Malvern. There are many more exam- 
ples that might be given, but these are enough. 
There is another mural plant, viz. the Wallflower, which ap- 
pears to be confined solely to artificial erections or ruins, not 
only here but also on the Continent. Its habitat in France is 
sur les vieux murs; 1 Germany, auf alten Gemduern im Rhein- 
thale (on old walls in the Rhine Valley). Where is the native 
country of this plant? In Europe, or in Africa, or in Asia? It 
will be difficult to fix its solwm natale by its habitats. We know 
something of its history. It was a favourite flower of old, as it 
still is; it was cultivated then as it is now. It may have mi- 
grated from the garden on to the garden-wall, and hence to the 
castle, to the church-tower, and to similar places. But who is 
to decide the question of its nativity? Have we any data for 
the adjustment of the conflicting claims of England, Germany, 
and France? Enough has been advanced to show that nativity 
and spontaneity, as these terms are generally applied, are not 
synonymous or convertible words. We can ascertain the latter 
character ; the former, in many cases, is beyond our ken. The 
period when these were introduced, if they were introduced, is a 
remote one; and all attempts to ascertain the quo and the quo- 
modo will be futile. 
In fine, it appears now to be impossible to ascertain the nati- 
vity of a large portion of our plants. Their number is increas- 
ing, and will probably continue to increase. We know the his- 
tory and the geography of the recent importations, and there is 
no reason for depreciating well-directed efforts to obtain as 
much information respecting the migrations of plants which 
have been established here for hundreds and thousands of years. 
. But who can tell when the Yew, or the Ash, or the Poplar, or 
the Chestnut, or the Pine were introduced, if they were intro- 
duced? We do not depreciate the investigation of such sub- 
