SICT. XXVII. DISTRIBUTION OF PLANTS. 265 



is concerned. In ascending the mountains of the torrid 

 zone, the richness of the tropical vegetation diminishes 

 with the height ; a succession of plants similar to, though 

 not identical with, those found in latitudes of corre- 

 sponding mean temperature takes place ; the lofty for- 

 ests by degrees lose their splendor, stunted shrubs suc- 

 ceed, till at last the progress of the lichen is checked by 

 eternal snow. On the volcano of TenerifFe there are 

 five successive zones, each producing a distinct race of 

 plants. The first is the region of vines, the next that 

 of laurels ; these are followed by the districts of pines, 

 of mountain broom, and of grass ; the whole covering the 

 declivity of the peak through an extent of 11,200 feet of 

 perpendicular height. 



Near the equator, the oak flourishes at the height of 

 9200 feet above the level of the sea, and on the lofty 

 range of the Himalaya, the primula, the convallaria, and 

 the veronica blossom, but not the primrose, the lily of 

 the valley, or the veronica which adorn our meadows : 

 for although the herbarium collected by Mr. Moorcroft, 

 on his route from Neetee to Daba and Garlope in Chi- 

 nese Tartary, at elevations as high or even higher than 

 Mont Blanc, abounds in Alpine and European genera, 

 the species are universally different, with the single 

 exception of the rhodiola rosea, which is identical with 

 the species that blooms in Scotland. It is not in this 

 instance alone that similarity of climate obtains without 

 identity of productions ; throughout the whole globe, a 

 certain analogy both of structure and appearance is fre- 

 quently discovered between plants under corresponding 

 circumstances, which are yet specifically different. It 

 is even said that a distance of 25 of latitude occasions a 

 total change, not only of vegetable productions, but of 

 organized beings. Certain it is, that each separate re- 

 gion both of land and water, from the frozen shores of 

 the polar circles to the burning regions of the torrid 

 zone, possesses a Flora of species peculiarly its own. 

 The whole globe has been divided by botanical geogra- 

 phers into twenty-seven botanical districts differing al- 

 most entirely in their specific vegetable productions ; the 

 limits of which are most decided when they are sepa- 

 rated by a wide expanse of ocean, mountain-chains, 

 Z 



