38 LAMTENG VILLAGE. Chap. XIX. 



species have migrated, the causes that favour their migra- 

 tions, and the laws that determine the types or forms of 

 one region, which represent those of another. A glance at 

 the map will show that Sikkim is, geographically, peculiarly 

 well situated for investigations of this kind, being centri- 

 cally placed, whether as regards south-eastern Asia or the 

 Himalayan chain. Again, the Lachen valley at this spot is 

 nearly equi- distant from the tropical forests of the Terai 

 and the sterile mountains of Tibet, for which reason 

 representatives both of the dry central Asiatic and Siberian, 

 and of the humid Malayan floras meet there. 



The mean temperature of Lamteng (about 50°) is that 

 of the isothermal which passes through Britain in lat. 52°, 

 and east Europe in lat. 48°, cutting the parallel of 45° in 

 Siberia (due north of Lamteng itself), descending to lat. 42° 

 on the east coast of Asia, ascending to lat. 48° on the west 

 of America, and descending to that of New York in the 

 United States. This mean temperature is considerably 

 increased by descending to the bed of the Lachen at 8000 

 feet, and diminished by ascending Tukcham to 14,000 feet, 

 which gives a range of 6000 feet of elevation, and 20° of 

 mean temperature. But as the climate and vegetation 

 become arctic at 12,000 feet, it will be as well to confine 

 my observations to the flora of 7000 to 10,000 feet; of 

 the mean temperature, namely, between 53° and 43°, the 

 isothermal lines corresponding to which embrace, on the 

 surface of the globe, at the level of the sea, a space varying 

 in different meridians from three to twelve degrees of 

 latitude.* At first sight it appears incredible that such a 

 limited area, buried in the depths of the Himalaya, should 

 present nearly all the types of the flora of the north 



* On the west coast of Europe, where the distance between these isothermal lines 

 is greatest, this belt extends almost from Stockholm and the Shetlands to Paris. 



