On the State of Vegetation on high Mountains, 26*9 



at one time : a humble hill continued between two valleys, 

 a ridge of rocks, and some steps, which the traveller passes 

 over in a few instants, are the insurmountable barriers 

 which nature has raised between things which it has thought 

 proper to separate. 



Among these different causes of separation, one more ap- 

 parent seems at first to direct all the rest: it is the eleva«* 

 tion of the different stages of mountains; every hundred 

 metres of height lower the temperature about half a degree 

 of the common division of our thermometers ; and if we 

 take as the term of cold that which generally suspends the 

 progress of vegetation, the eternal ice with which the sum- 

 mits 'are charged will represent the ice also eternal with 

 which the pole is covered ; and each hundred metres of ver- 

 tical elevation will correspond to a degree of the distance 

 of the mountain from the pole. 



It is on this short scale that the phaenomena of the cli- 

 mates which succeed each other on the surface of the earth 

 are presented ; the circumstances are different, but the re- 

 sults are nearly the same: on the one hand, the increase of 

 the cold is accompanied with a shortening of the column 

 of air; on the other, with an obliquity of the rays of the 

 sun. The vegetables, however, are distributed in a manner 

 nearly similar; and th?s conformity teaches us to exclude 

 from the number of the causes which act on this distribu- 

 tion, those which are not common to the two scales on 

 which they have been executed by nature. Thus, in the 

 Alps and the Pyrenees trees stop at the absolute elevation 

 of 2400 or 2500 metres, as they do about the 70th degree 

 of latitude; and the band of the mountains occupied by 

 these large vegetables is divided into as many particular 

 bands as the trees constitute different species : oaks remain' 

 at the bottom; the beech occupies the mean heights; and 

 above these are the pitch-pine and the yews, which soon 

 give place to the pines, and these pines both in the Pyre- 

 nees and the Alps are those of Scotland and of Riga: 

 while the latter chain possesses also the cembra and the 

 larch, which are foreign to the former; but it wants the ce- 

 dar which grows on the Lebanon, and which would, no 

 doubt, thrive in our mountains of Europe, had nature placed 

 them there, as it has done on the mountains of Asia. But 

 such is the mystery of the original dissemination of vege- 

 tables, that nature seems, in turn, indifferent in regard to 

 the similitude of places and the distances by which they 

 are separated ; sometimes placing in similar climates the 

 plants of countries the most distant from each other, and 



sometimes 



