| land above the level of the sea. 
| portant element in all just calculations respect- 
| ing vegetable physiology, the making of planta- 
| tions, and the rotation of crops. 
native of Syria, but flowers freely in almost any 
common garden ground in England, and is one 
of the most beautiful of our ornamental shrubs. 
| The well-defined and thoroughly-established vari- 
eties of it are six,—the purple-flowered, the red- 
flowered, the white-flowered, the striped-flowered, 
the double white, and the double purple, and all 
attain a height of eight feet, and bloom in August 
and September. Their branches are smooth, 
whitish, and not very numerous; their leaves 
are ovate-spear-shaped, serrated, of a pleasant 
green, and growing on short irregularly-situated ' 
footstalks; and their flowers have longer foot- 
stalks than the leaves, and come out with them 
from the sides of the young shoots in such a 
manner as often to garnish the young shoots over 
their whole length. The Alihea frutex is easily 
| propagated from either seeds, layers, or cuttings. 
ALTITUDE or Exevation. The height of 
This is an im- 
Vegetation, in 
ascending above the level of the sea, undergoes 
modifications analogous to those which attend 
_ its progress from the equator to either pole. Thus 
| 600 feet of altitude above sea-level is found to 
be equal, in its influence upon both indigenous 
and cultivated vegetation, to a removal of one 
degree from the equator, or between 60 and 70 
miles toward the north or south; so that a 
situation only a few feet above sea-level in the 
latitude of Edinburgh is equal, in its genial 
powers, to a situation about 3,000 feet above 
sea-level in the latitude of London, and the height 
of 4,000 or 5,000 yards in the hottest parts of the 
globe produces changes as distinct as the 2,000 
leagues or more which lie between the equator 
and the polar regions. Other elements than mere 
altitude, indeed, contribute to the aggregate char- 
acter of climate,—particularly the direction of 
slope or exposure, the angle of elevation, the low- 
ness or mountainousness of surrounding country, 
nearness or distance from the saline vapours of 
the ocean, favourableness or unfavourableness of 
surrounding surface for natural ventilation, the 
direction, force, and temperature of the prevail- 
ing winds, the amount and modifications of at- 
mospheric moisture, the mineral constitution and 
mechanical condition of both the immediate and 
the surrounding soil, and the general prevalence 
of marshiness or aridity, of natural forests or 
cultivated fields, of pastoral grounds or arable 
farms ; and so greatly do these elements and some 
others modify temperature, that dsothermal lines, 
or lines of equal heat as drawn by observation 
around the globe, are found to make very sur- 
prising curvatures, and to vary, in numerous in- 
stances, to the enormous extent of eight or ten 
geographical degrees [see article ChimaTE]; yet 
altitude alone is so great an element, and exerts 
of itself so powerful an influence, that, in any 
one country or series of contiguous countries of 
ALTITUDE. 
tolerably uniform character in soil and cultiva- 
tion, it may fairly be regarded as the equivalent 
of climate, in the proportion of 600 feet of alti- 
tude to one degree of latitude. The reason of 
this is, that altitude involves diminution of heat, 
dryness of air, protracted duration of light, a de- 
crease of depth in the volume of the air, and a 
scarcity of those substances which are produced 
by the decomposition of organic bodies. 
The higher we ascend, the shallower the upper 
stratum of air becomes; whence the excessive 
cold at great heights; for it is the action of the 
atmosphere upon the rays of light which extracts 
the caloric from them, and we know that the 
extraction of caloric diminishes in proportion as 
the mass of air traversed by the rays is shallower ; 
but, on the other hand, the light is purer and 
more active, just as if caloric was really a simple 
transmutation of light, as some naturalists have 
conceived it to be. The weight of the atmo- 
sphere, which at the level of the sea supports a 
column of mercury 28 inches high, diminishes as 
we ascend; so that at the elevation of 6,000 yards 
it will only support a column of 13 inches and 
some lines high. A consequence of this fact is, 
that the vaporization of fluids takes place on high 
mountains at a very low degree of heat. Not- 
withstanding this, however, the decrease of heat 
is so great, that the ambient air is very slightly | 
impregnated with moisture. It is true that 
heights have not the long days of the polar re- 
gions ; but they receive the rays of the sun earlier 
than the plains, and are quitted later by them, so 
that their nights are shorter than in levels. In 
fine, substances which have been formed by the 
decay of organized bodies, are rare on mountains, 
the rains as well as the waters of the springs dis- | 
solving them, and carrying them away as they 
run off into the valleys. 
but these causes united must act powerfully upon 
vegetation. 
cause the plants on mountains to transpire co- 
piously ; the severity of the cold, the dryness of 
the atmosphere, the shortness of the nights, the 
scarcity of humus, will impede the enlargement 
of their leaves, and the growth of their stems ; 
the strength of the light, and the protracted du- | 
ration of the day, will accelerate the induration | 
of all the parts of their frame. 
The course of vegetation on mountains had not 
escaped the penetration of Tournefort. At the 
foot of Mount Ararat he had observed the plants 
which grow in Armenia; a little higher, those of 
Italy and France; above, those of Sweden; and 
upon the summits, those of Lapland. Observa- 
tions of the same kind had been subsequently 
made on Mount Caucasus, the Alps, the Pyrenees, 
and other mountains of the Old continent. Every 
botanist had learned that many of the alpine - 
plants, that is to say, plants which grow on the 
various high lands of Europe and Asia, are like- 
wise met with at Spitsbergen, in Nova Zembla, 
Lapland, and Kamschatka. Swartz had discoy- 
It cannot be doubted, | 
The slightest degree of heat will | 
aa 
| 
: al 
