308 
GEOGRAPHICAL SITUATION OF PI A NTS. 
ful flowers. The richest fruits and spices and the most valua 
Die medicinal plants, are found here. In ascending the mount- 
ains of the torrid zone, as the temperature varies, each section 
has its own distinct plants ; and we find in succession the pro- 
duction of every region from the equator to the poles. 
320. The productions of the southern temperate zone diflei 
much from those of the northern temperate, owing to many 
causes, which impede the dissemination of plants, variations va 
temperature from elevation, &c. The antartic flora terminates 
at Terra del Fuego and Kerguelen's land ; — while in the arctic 
regions no land has yet been discovered entirely destitute of 
vegetation, in the antarctic utter desolation prevails, not even 
a lichen clings to the frost-covered rocks. Perpetual snow 
comes to a lower latitude in the southern frigid than the north- 
ern frigid zone. Cockburn Island, one of the South Shetland 
group, in south latitude 60°, contains the last vestiges of vege- 
tation ; while in the same degree of latitude in North Ameri- 
ca, lands are inhabited and cultivated. 
321. As the mountains of the torrid zone afford every variety 
of climate between their base and their summit, so they are 
capable of producing all the vegetables of every climate ; — but, 
as latitude increases, temperature diminishes, so, generally 
speaking, the productions, as we proceed from the tropic north- 
ward or southward, correspond with the elevation at which the 
same plants will grow upon a mountain within the tropics. 
Every plant requires, other circumstances being the same, the 
same mean annual temperature for example : the plantain- 
tree and sugar-cane require a mean annual heat of from eighty- 
two to eighty-three degrees of Fahrenheit ; but seventy degrees 
of mean annual heat is not found beyond the twenty-seventh 
degree of latitude ; consequently, the plantain and sugar-cane 
will not ripen in the open air in a higher latitude ; and this 
Baron Humboldt has found to correspond with the hight of 
three thousand feet under the equator. Cotton will not flourish 
without sixty-eight degrees of heat ; this is not found beyond 
thirty-four degrees of latitude, which corresponds with about 
three thousand six hundred feet of elevation at the equator. 
The same reasoning applies to all other plants, with the excep- 
tions arising from warm valleys, moisture of air, and richness of 
soil. 
Feet above the level of the sea. 
The highest spot on which man ever trod 19,400 
The highest limit of the hchen plant 18,225 
The lowest limit of perpetual snow under the equator ... 15,730 
* For explanation of mean annual temperature, see note, page 142. 
320. Southern temperate zone. — 321. Production of every region found in aseen ing mcjntainsof 
the torrid zone — Elevation produces similar effects on vegetation, as distance from tl^ eciuator 
