RHODODENDRON'S OF EUROPE. 
427 
from the equator augments. The rhododendron of Lapland 
grows also at eight or nine hundred toises lower than the 
rhododendron of the Alps and the Pyrenees. We were 
surprised at not meeting with any species of befaria in the 
mountains of Mexico, between the rhododendrons of Santa 
Le and Caracas, and those of Florida. 
In the small grove which crowns the Silla, the Befaria 
ledifolia is oidy three or four feet high. The trunk is 
divided from its root into a great many slender and even 
verticillate branches. The leaves are oval, lanceolate, glau- 
cous on their inferior part, and curled at the edges. The 
whole plant is covered with long and viscous hairs, and 
emits a very agreeable resinous smell. The bees visit its 
fine purple flowers, which are very abundant, as in all the 
alpine plants, and, when in full blossom, they are often 
nearly an inch wide. 
The rhododendron of Switzerland, in those places where 
it grows, at the elevation of between eight hundred and a 
thousand toises, belongs to a climate, the mean temperature 
of which is + 2° and — 1°, like that of the plains of Lap- 
land. In this zone the coldest months are— 4°, and — 10°: 
the hottest, 12° and 7°. Thermometrical observations, made 
at the same heights and in the same latitudes, render it 
probable that, at the Pejual of the Silla, one thousand toises 
above the Caribbean Sea, the mean temperature of the air 
is still 17° or 18° ; and that the thermometer keeps, in the 
coolest season, between 15° and 20° in the day, and in the 
night between 10° and 12°. At the hospital of St. G-othard, 
Bituated nearly on the highest limit of the rhododendron of 
the Alps, the maximum of heat, in the month of August at 
noon, m the shade, is usually 12° or 13 c ; in the night, at the 
same season, the air is cooled by the radiation of the soil 
down to + 1° or — 1'5°. Under the same barometric pres- 
sure, consequently at the same height, but thn’ty degrees of 
latitude nearer the equator, the befaria of the Silla is often, 
at noon, in the sun, exposed to a heat of 23° or 24°. The 
greatest nocturnal refrigeration probably never exceeds 7”. 
We have carefully compared the climate, under the influence 
of which, at different latitudes, two groups of plants of the 
same family vegetate at equal heights above the level of the 
sea. The results would have been far different, had we com- 
