908 GEOGEAPHICAL SITUATION OP PLANTS. 



ful HoAvers. The richest fruits and spices and the most valiia 

 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 2)roductions of the souiliern temjperate zone diiFer 

 much from those of the northern temperate, owing to many 

 causes, wdiich impede the dissemination of plants, variations in 

 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 w^e 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 teinjperature / - 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 wliich man ever trod 19,400 



The highest limit of the lichen 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 ascending mountains of 

 the torrid zone — Elevation produces similar effects on vegetation, as distance from tlie equator 



