]8 VEGETATION OP HIGH MOUNTAINS. 



reign predominant over all others j this is, elevation above the 

 level of the sea. In every 100 inches in height, the temperature 

 falls about half a degree of our thermometers. After that de- 

 gree of cold, which generally puts a stop to all vegetation, an 

 eternal frost prevails on the summit of these Alps, as at the 

 100 yards poles, and every 100 metres of vertical elevation, corresponds 

 vaTent uTa dc- near ty to one degree of the distance at which the mountain is 

 gree of lati- placed from the pole. 



J" e * By this scale, the various phenomena of different climates in 



Two causes of , , , .. - . . .. _, 



thedistribu- our globe may be easily understood : circumstances may differ, 



tion of vege- but the general results will be nearly the same. While the in- 

 crease of cold is accompanied by a diminution of the column of 

 air, it is also affected by the obliquity of the rays of the sun, and 

 the distribution of vegetables, in all alpine countries, depends 

 principally on these two causes. 



Trees. Thus, in the Swiss Alps, and Pyrenees, trees cease to grow at 



about 2-400 or 2500 metres of actual elevation, as they do about 

 the /Oth degree of north latitude j and that circle these gigantic 

 vegetables occupy, is divided into several less bounds, which 

 have each their peculiar characteristics. At the foot of the 

 mountain we find the oak : in the middle region the beech : above 

 these the^r and yew succeed, which soon give place to the pine 

 (Pinus sylvestris L.). Along with this last mentioned tree, in the 

 Swiss Alps the larch and cembro (Pinus cembra L.) also grow wild, 

 which are unknown in the Pyrenees. The cedar of JLebanus would 

 probably thrive as well on these mountains, as on those of Asia, 

 had it been fixed there j but such is still the mystery of the ori- 

 ginal dissemination of vegetables, that Nature seems by turns, 

 indifferent to the similitude of places, or to the distance between 

 them j sometimes bringing together in the same climate, plants 

 of the most distant countries j and sometimes denying this con- 

 formity of vegetables to regions exactly alike, both in soil and 

 temperature. 



Jthododen- In tu ' s zone of trees, the rhododendron ferrugineum L. a little 



dron. . shrub peculiar to the mountains of Europe solely, is very abun- 



dant. It never descends into the plains, and can hardly be cul- 

 tivated In a garden, demanding its native air, soil, water, nay 

 snows, and even there only occupies particular spots. Nothing 

 is more beautiful when in flower, but nothing is more untrac- 

 table. In the Pyrenees it first appears at exactly 1600 metres 



of 



