CHAP. vn.J DISTRIBUTION OF PLANTS. 205 



occurring in this zone have each a marked flora, as the 

 cactus group in Mexico, the euphorbius or spurges in 

 Africa, and numerous succulent and fleshy plants in the 

 Asiatic region. The date-palm also constitutes a feature 

 of the arid region in Egypt. 



The Tropical Zone, extending from the isth degree on 

 each side of the equator to lat. 23°, having a mean annual 

 temperature of 7 3° to 7 9° Fahr., and a summer heat of 80° to 

 86° Fahr., is characterized by the abundance of tree-ferns 

 and numerous species of Ficus ; this zone is also the 

 head-quarters of the orders Piperacece and Melastomacece. 



Equatorial Zone, extending 15° on each side of the 

 equator, has a mean annual temperature of 79° to 85° 

 Fahr. ; the characteristic vegetation consists of palms, 

 bananas, arborescent grasses (as the bamboo, sugar-cane, 

 etc.), orchids, and spectes belonging to the order 

 ZingiheracecB, as the ginger plant, etc. 



Comparing the zones of altitude with those of latitude 

 the following gives a broad idea of the relative elevation 

 at which the groups previously mentioned occur. 



Equatorial Region of palms and bananas extend from 

 the sea-level to 2,000 feet. 



Tropical Region of tree-ferns and figs, 2,000 to 3,800 feet. 



Sub-tropical Region of myrtles and laurels from 3,800 

 to 6,000 feet. 



Warm Temperate Region of evergreen dicotyledonous 

 trees, 6,000 to 8,000 feet. 



Cold Temperate Region of deciduous dicotyledonous 

 trees, 8,000 to 9,500 feet. 



Sub-arctic Region of conifers, from 9,500 to 11,500 feet, 



Arctic Region, characterized by bright-flowered rhodo- 

 dendrons, 11,500 to 13,500 feet. 



