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biosphere, it is probable, that at the height of 

 Portillo, the roots of the pines draw their nourish- 

 .ment from a soil, in which, at a certain depth, 

 the thermometer rises at most to nine or ten 

 degrees. 



The fourth and fifth zones, the regions of the 

 retama and the gramina, occupy heights equal 

 to the most inaccessible summits of the Pyrenees. 

 It is the sterile part of the island, where heaps 

 of pumice stone, obsidian, and broken lava, form 

 impediments to vegetation. We have already 

 spoken of those flowery tufts of alpine broom 

 (spartium nubigenum), that form oases amidst a 

 vast sea of ashes. Two herbaceous plants, the 

 scrofularia glabrata, and the viola cheiranthi- 

 folia, advance even to the Malpays. Just above 

 a turf scorched by the heat of an African sun, 

 an arid soil is overspread by the cladonia pas- 

 chalis, to which the herdsmen often set fire, that 

 rolls to considerable distances. Toward the 

 summit of the Peak, the urceolarea, and other 

 plants of the family of the lichens, labour at the 

 decomposition of the scorified matter. By this 

 unceasing action of organic forces the empire of 

 Flora extends itself over islands ravaged by 

 volcanoes. 



In traversing the different zones of the vege- 

 tation of Teneriffe, we see that the whole island 

 may be considered as a forest of laurels, arbutus, 

 and pines, of which the border has scarcely been 



VOL. I. T 



