90 CLIMATE AND VEGETATION OF 



feet, and of vegetation at 14,500 ; whereas in lat. 35° 30' Dr. 

 Thomson found the snow line 20,000 feet in Karakorum, and 

 vegetation up to 18,000 feet — features common also to Sikkim in 

 lat. 28°. 



Of the Sikkim Khododendrons I have little further to say except 

 with reference to the individual species, and I shall therefore 

 arrange these in three groups, according to the elevations they 

 inhabit, adding such notes upon each as may prove useful in 

 their determination and assist in their cultivation. No species 

 that I am aware of extends much below 6000 feet in Sikkim, or 

 in the Himalayas generally, though, according to Mr. Griffith, 

 R. arhoreum is found below 4000 on some of the dry rocky 

 outer ranges of Bhotan. In this respect, however, the latter 

 country is very exceptional, and demands a passing notice. The 

 Khassya mountains, as I have elsewhere shown, shield the lower 

 ranges of Bhotan from the effects of the southerly monsoon ; they 

 rise to an average height of 5000 feet, extending (as the Gar- 

 rows, westward, and Jyntea hills, eastward) for about 250 miles 

 parallel to and 60 miles south of the Bhotan Himalaya, the inter- 

 vening valley being that of the Burrampooter river. The mon- 

 soon from the Bay of Bengal is in this longitude a S.S.W. one, 

 and after traversing 200 miles, partly of the Sunderbunds and 

 partly of a very peculiar marsh district called the J heels, it dis- 

 charges an amoimt of water on the abrupt southern face of the 

 Khassya which, as a rain-fall, I believe has no parallel in the 

 world, amounting to between 400 and 500 inches a-year. Sud- 

 denly deprived of one-third of its water, the current pursues its 

 course northward, traversing 30 miles or so of hills, whereby it is 

 cooled ; while it is again warmed in the moist valley of Assam. 

 What is thence carried on to the Bhotan Himalaya is not con- 

 densed on the mountains till it reaches a considerable elevatioUj 

 5000 feet and upwards, where it is cooled and deposits moisture 

 abundantly. The Bhotan Himalaya is therefore very dry below 

 50OO feet, and humid above that, but never so nmch so as 

 Sikkim. 



R. arhoreum is found at 4500 feet on the Khassya (but not 

 near the southern edge of the range), and ascends to 7000 feet* 

 There are several other Khassya species, all avoiding the southern 

 parts, though one of them descends to 2000 feet on the north 

 flank. Most of the species, as well as those of the Malay 

 peninsula, Java, and Borneo, belong to the same section with 

 R. cinnaharinum, having comparatively long tubes to the corolla 

 and small calyces, or none. 



The Borneo species* gathered by Mr. Low on Kini Balu, 



* Many of these species will be figured shortly in Sir Wi J. Hooker's 

 * Icones Plantarum.' 



