THE NORTHERN VEGETATION COMPARED, ETC. 139 



plants ; for though analogous, the flora of the high North is by no 

 means identical with that of the most elevated Alpine ridges, over 

 which vegetation continues to extend. The influence of atmospheric 

 pressure seems to me particularly evinced in the great, I may say 

 the prevailing number of Alpine species endowed with a volatile fra- 

 grance which adds so much to the sweet and soothing influence of 

 mountain rambles ; whilst the northern species, however similar to 

 those of the Alps, partake more or less of the dullness of the heavy 

 sky under which they flourish.* 



Whatever may be the intensity of other causes, and even when 

 they are most uniform, the chemical nature of the soil acts perhaps 

 as powerfully as the physical conditions under which the plant may 

 grow. To be fully impressed with the important influence of the soil 

 we need only be familiar with the diflerences noticed in the growth 

 of wheat or other grains in different soils, or with the different aspect 

 of pastures on rich or poor grounds, and to trace the same modifica- 

 tions through any small tract of land with the view to understand 

 similar changes over wider countries. f 



* It would be a mistake to ascribe to reduced atmospheric pressure the peculiar aspect 

 of most plants in the higher Alps, as they are undoubtedly more influenced by the 

 temperature, and especially by the pressure of the snow of those high regions. These 

 plants are commonly covered with a thick and close down, which reminds us of the soft 

 fur of the northern animals ; they creep for the most part attached to the compact and 

 tenacious soil among the clefts of rocks, where their roots can penetrate and where they 

 find shelter. Several of them have fleshy and succulent leaves, filled with liquid, 

 derived rather from the atmosphere, than from the stony and dried soil upon which we 

 generally find them. These phenomena of Alpine vegetation occur successively at a 

 less considerable elevation the more we advance northwards, and show themselves on 

 the plains towards the polar regions, where the temperature agrees with that of the 

 high Alpine summits. The fact that many plants of the highest summits live very well 

 at the foot of the glaciers which descend into the htwer valleys, would seem to show 

 that atmospheric pressure has only a limited influence upon Alpine plants ; but the mo- 

 ment we have satisfied ourselves that the most fragrant of these species never prosper 

 below, we must admit that the relation between fragrance and atmospheric pressure to 

 which I have alluded above, is well sustained. The Alpine plants are, it is well known, 

 very difficult to cultivate ; Mr. Vaucher, at Fleurier, assisted by Mr. Lesquereux has 

 however succeeded in bringing together a magnificent and numerous collection of spe- 

 cies of the high Alps. In order to preserve them, they took care to harden and press 

 the soil, or to introduce small blocks of limestone into it, and to cover them with snow 

 in the spring, but especially to press the roots very often into the ground in the spring, 

 as they are otherwise pushed out after every frost, and perish in a single day if care be 

 not taken to put them again without delay into the ground. 



fThe chemical elements of the soil seem, however, to have less influence upon the 

 geographical distribution of the large vegetables or phaenogames, than upon the cryp- 



