Description of the Landes of Acquitania. ri 
on the west than on the east of France.* If we compare the wes- 
tern and eastern provinces, we shall find that the former are very 
little elevated above the level of the ocean; for, according to De- 
candolle, even at a considerable distance from the sea, they do not 
attain an elevation of more than 100 metres, while on the contrary, 
the eastern provinces, surrounding the great mountain chains, have 
generally from 4 to 500 metres of elevation. 
De Humboldt gives for the plains of central France and Lom. 
bardy, 80 toises, 511.57 English feet ; and though, as Decandolle 
has remarked, near Belgium the degree of elevation diminishes, 
yet there the temperature is also sensibly cooled by the second 
cause that produces such a change, namely, distance from the equa- 
tor. The plains at the foot of the eastern Pyrenees, do not attain 
an elevation of more than 63 feet near Perpignan, but they rapid- 
ly rise, attaining at Arles 908.03 feet, and at Foix 1214.97 feet. 
‘he great plain of Thoulouse is about 466.81 feet, and this will 
average the plains of Gascony, rising at Tarbes 959.15 feet, at 
Luz to 2423.65 feet: the plain of the Landes is 328.0899 English 
feet above the level of the sea.t The influence of the proximity 
of the sea, in equalizing the mean annual heat, and the effect of the 
difference of physical aspect on the opposite sides of the continent, 
on the isotheral and isocheimal lines, render it highly probable, 
that even with an equal mean temperature, the distribution of the 
plants on the two sides would be different. 
In the west a slight change in the Graminz takes place about the 
line of cultivation of the maize, or in lat. 46°. The Panicum dactylon, 
more abundant on the shores, is met with in the woods, south of Poi- 
tiers; the Lolium perenne is replaced by the Aira media: these 
are soon followed by other grasses, as the Alopecurus utriculatus, 
Andropogon provincialis, Agrostis capilaris, A. stolonifera, Poly- 
pogon monspeliensis, Digitaria stolonifera, D. ciliaris, Schismus 
marginatus, &c. &c. At Tours, the beautiful Nymphaz alba wan- 
ders from deep ponds to flower in the smallest collections of water ; 
the Erigeron canadense will occupy sometimes one side of a ditch, 
while its contemporary, the E. campestre, will be seen on the 
other. ‘They are succeeded near Thoulouse by the Erigeron glu- 
tinosum and E. Villarsii, accompanied by a curious plant, the Mo- 
mordica Elaterium: the Quercus nigra is met with every where in 
the west as far as Nantes, but is unknown in all the east; the 
Menziesa Dabeoci (Erica Dabeoci, Eng. Bot.) is likewise met with 
in the west, where plants of the hot climates are also seen wander- 
* Mr Arthur Young had remarked, that if a line be drawn across the most 
northerly points of cultivation of the olive, maize, or vine tree, three nearly parallel 
lines are obtained, which all approximate to the north on the eastern side; pre- 
cisely the inverse of what the French naturalists have observed with respect to 
the indigenous plants. 
+ These altitudes have been all reduced to the English standard, through the 
Kindness of Mr Buchanan, from Reboul and Vidal’s trigonometrical measure- 
ments of the Pyrenees, and the barometrical observations of Ramond, Charpen- 
tier, and D’Aubuisson. 
