GEOGRAPHICAL SITUATION. 295 



kingdom, we see the powerful effects of light and heat. Feeble 

 in the polar regions, vegetation acquires strength as we approach 

 towards the equator, where the light of the sun is vivid, and its 

 heat, permanent and intense. 



The centre of the frigid zone is entirely destitute of vegeta- 

 tion. After passing the arctic circle, we find on the borders 

 of the temperate zone, a few species of plants, chiefly lichens, 

 mosses, and ferns, also a'^ew shrubs and berries. In the heat 

 of a polar summer, the growth of plants is rapid ; Lapland is 

 the only country within this zone where any kind of grain can 

 be raised. 



The productions of the temperate zone gradually alter in 

 character as we approach the tropics. Humboldt has divided 

 the temperate zone, with respect to productions, into three 

 regions ; the cold, the temperate, and warm regions. In the 

 cold region, grain may be raised to advantage, and berries 

 grow in abundance. In the temperate region, the wine grape , 

 grain f and fruits of many kinds, are cultivated in their greatest 

 perfection. The warm region produces olives, jigs oranges 

 and lemons. 



The variety of plants in the torrid zone is very great. Trees 

 are more numerous in proportion to other plants, than in the 

 temperate zones ; the same tribes which are there slender and 

 humble plants, here spread into lofty trees, many of which are 

 adorned by large and beautiful flowers. The richest fruits and 

 spices, and the most valuable medicinal plants are found here. 

 In ascending the mountains of the torrid zone, as the tempera- 

 ture varies, each section has its own distinct plants, and we find 

 in succession, the production of every region from the equator 

 to the poles.* 



As the mountains of the torrid zone afford every ^variety of 

 climate between their base and their summit, so they are capa- 

 ble of producing all the vegetables of every climate ; but as 

 the temperature diminishes, as the latitude increases, so, gene- 

 rally speaking, the productions, as we proceed from the tropic 

 northward or southward, correspond with the elevation at 

 which the same plants will grow upon a mountain within the 

 tropics. Every plant requires other circumstances alike ; the 

 same mean annual temperature,f for example. The magnifi- 

 cent plantain tree and valuable sugar cane require a mean 

 animal heat of from 82 to 73 degrees ; but 73 degrees of mean 



t JH? explanation of mean annual temperature, see note under vines, Lec- 



ture 22. 



Plants of the frigid zone Temperate rone Torrid zone Production of 

 every region found in ascending mountains of the torrid zone. 



