114 CLIMATE AND VEGETATION OF 



English spring months is the great obstacle to the cultivation of 

 many Himalayan plants ; it is not hence to be inferred that 

 there is no similar amount of radiation in the Himalaya, for, on 

 the contrary, in April its amount is much greater than in 

 England, equalling 13° of difference frequently, and I have seen 

 16° at 7500 feet; but the minimum temperature at the time is 

 51°, and the absolute amount of cold hence immaterial. The 

 mean minimimi of London is 38"0°, and when lowered 5*5° by 

 radiation the consequent cold is very considerable. Mr. Daniell, 

 in his admirable essay on the climate of London (the perusal of 

 which first gave me an interest in these pursuits), mentions +17° 

 as the maximum effect of nocturnal radiation ever observed by 

 him ; I have had +20° from the surface of snow, and I have 

 registered + 13-0°, + 14-0°, + 15-5°, and + 16-0° in April at 

 Darjiling ; nearly as much at 6000 feet in February ; once 

 + 12-0°, twice +13-0°, and once + 14*2° in September at 15,500 

 feet; +10° in October at 16,800 feet ; + 1 10°, + 1 2-0°, and 

 nearly +13-0° in January at 7000 feet; +10° to + 14-5° 

 repeatedly in February at that elevation, and + 12° to + 14"7° 

 at 10,000 feet in November on several occasions. 



To conclude, though nocturnal radiation does occur frequently, 

 and lias on the whole a much more ])owerful effect in Sikkini 

 than in England, I doubt if the mean effect of all the months in 

 Sikkim would equal that of London, from so many more nights 

 being cloudy, which cloudy atmosphere and the comparatively 

 high temperature of the nocturnal radiating months are what a 

 Himalayan vegetation wants in England. 



Winds. — Of the Himalayan winds there is little to be said 

 affecting the horticulturist. The southerly moist, warm current 

 is perennial, except during the spring months, when occa- 

 sional S.AV. squalls or moderate day winds blow. The nights 

 are usually calm, or return cool winds sweep gently down 

 the valleys. The northerly winds are said to bring snow ; in 

 December to February they appear to me to be local phenomena, 

 and are under currents from the snowed regions, which condense 

 and freeze the lower strata of the main current. Heavy gales 

 occur at the equinoxes in the Himalaya as all the world over, 

 but I have never experienced cyclones or hurricanes. Mid- 

 summer and midwinter are also generally characterised by storm 

 and rain. 



Atmospheric presstire. — It has long been surmised that an 

 alpine vegetation may owe some of its peculiarities to the dimi- 

 nished atmospheric pressure ; and that the latter being" a condition 

 which the gardener cannot supply, he can never successfully 

 cultivate alpine plants in general. I know of no foundation for 

 this hypothesis ; many plants, natives of the level of the sea 



