96 Mr. R. Spruce on the Musci and Hepatice of the Pyrenees. 
that is, by certain plants which constitute a marked feature in 
them, it would seem at first sight a great advantage could we se- 
lect in every country the same species for this purpose ; but a little 
research will suffice to show us the impracticability of this. To 
go no farther than the Alps ; near as they are to the Pyrenees, and 
similar as their vegetation is in many respects, there are yet im- 
portant differences. While, for instance, there is no tree in the 
Alps above the region of the spruce-fir (Pinus Abies, L.), in the 
Pyrenees there is above this a broad and well-marked belt of 
Scotch fir (Pinus* sylvestris, L.). Again, there is in the Alps, 
above the limit to which the oak ascends, a zone in which the 
birch (Betula alba, L.) is the predominant tree; but in the 
Pyrenees the birch is excessively rare ; indeed I do not at this 
moment recollect having anywhere seen it where I could be cer- 
tain it had not been planted, and I perceive Mr. Bentham in- 
cludes it in his catalogue with a mark of doubt. It would also” 
be quite impossible to define any of our climatal zones in the 
Pyrenees by the distribution of the heaths, as has been done for 
the British Isles by Mr. Watson in his ‘ Cybele Britannica.’ The 
only “ heath-clad hills” I have seen in the Pyrenees, reminding 
me of our English and Scottish hills, are some of the lower 
mountains around Bagnéres-de-Bigorre, and here the prevailing 
species is Hrica vagans, though Calluna vulgaris occurs also, 
sparingly. The latter species seems never to penetrate far into 
the mountains. Again, Erica tetraliz is not found at all in the 
Central or Eastern Pyrenees, but only in the Western. The 
only heath I have remarked near Bagneres-de-Luchon is Erica 
cinerea. E. arborea is abundant in the valley of Argélez and its 
tributary valleys (Castelloubon, &c.), but is absent from the Cen- 
tral Pyrenees, while it reappears in several parts of the Eastern. 
It has been shown by M. des Moulins (“ Etat de la Végétation 
sur le Pic du Midi de Bigorre, &e. ;” ‘Recueil des Actes de 
VAcadémie Royale de Bordeaux,’ 1844), that several species of 
thistles occupy zones of altitude in the Pyrenees which are easily 
ascertained, and he has actually constructed a scale of the dis- 
tribution of fourteen species in the Pyrénées Centrales, showing 
the altitudes at which they appear and disappear. But were 
this scale taken as the basis of a climatal arrangement (which M. 
des Moulins by no means proposes), how would it assist us im 
comparing the flora of the Pyrenees with that of Lapland, where 
according to Wahlenberg, “Cardwi in sylvis admodum rari, 
omnesque fere inermes sunt. De cetero quoque plante vel 
frutices aculeati in Lapponia non crescunt, &c.” ? 
In comparing two distant portions of the earth’s surface with 
each other, in both of which the same plant is extensively distri- 
buted, we are not hence to conclude that the zone which it oc- 
