250 VEGETABLE ZONES. SECT. XXVI. 



part of the globe of equal extent, for that rich and luxuriant 

 region discovered by Dr. Livingstone has yet to be explored 

 botanically. Very few social plants, such as grasses and heaths 

 that cover large tracts of land, are to be found between the 

 tropics, except on the sea-coasts and elevated plains. Some 

 exceptions to this, however, are to be met with in the jungles of 

 the Deccan, &c. In the equatorial regions, where the heat is 

 always great, the distribution of plants depends upon the mean 

 annual temperature ; whereas in temperate zones the distribution 

 is regulated in some degree by the summer heat. Some plants 

 require a gentle heat of long continuance, others flourish most 

 where the extremes of heat and cold are greater. The range of 

 wheat is very great ; it may be cultivated as far north as the 

 60th degree of latitude ; but in the torrid zone it will seldom 

 form an ear below an elevation of 4500 feet above the level of 

 the sea from exuberance of vegetation ; nor will it ripen gene- 

 rally above the height of 12,000 feet ; in Tibet it ripens at a 

 still greater elevation. Colonel Sykes states that in the Deccan 

 wheat thrives as low as 1800 feet above the sea. The best wines 

 are produced between the 30th and 45th degrees of north lati- 

 tude. With regard to the vegetable kingdom, elevation is equi- 

 valent to latitude as far as temperature is concerned. In 

 ascending the mountains of the ton-id zone, the richness of the 

 tropical vegetation diminishes with the height ; a succession of 

 plants similar to, though not identical with, those found in lati- 

 tudes of corresponding mean temperature takes place ; the lofty 

 forests by degrees lose their splendour ; stunted shrubs succeed ; 

 till at last the progress of the lichen is checked by perpetual 

 snow. On the volcano of Tenerifle there are five successive 

 zones, each producing distinct families of plants. The first is the 

 region of vines, the next that of laurels ; these are followed by 

 the region of pines, of Ericas or heaths, of grass ; the whole 

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

 feet of perpendicular height. 



Near the equator oaks flourish at the height of 9200 feet 

 above the sea ; and, on the lofty range of the Himalaya, the 

 primula, the convallaria, and the veronica flower, but not the 

 primrose, the lily of the valley, or the veronica, which adorn our 

 meadows ; for, although the herbarium collected by Moorcroft, 

 on his route from Neetee to Daba and Gartope in Chinese Tar- 



