82' VEGETATION. 



as Indigofera and Dcsmodium, Ranunculacece (TkaUcinim, Anemone, 

 Delphinium, Aconitum, etc ), UmbelH/erce, Caryophyllece, Labiatce and 

 Graminece increase in numbers as we advance into the interior. 

 The air becomes drier, and from the increased action of the sun 

 the temperature does not diminish in proportion to the elevation, 

 the summers being warmer, though the winters are colder. The 

 forests at the same time become more open, and are spread less 

 uniformly over the surface, the drier slopes being bare of trees, 

 and covered with a luxuriant herbaceous vegetation. It is only in 

 the upper part of the valley of the Tista, however, above the 

 junction of the Lachen and Lachung, that this change becomes marked ; 

 and from the rapidly increasing elevation, not only of the sur- 

 rounding mountains, but of the floors of the valleys, it proceeds 

 with great rapidity, and the temperate soon gives place to an 

 Alpine flora. 



" The sub-Alpine zone in Sikhim scarcely begins below 13,000 

 feet, at which elevation a dense rhododendron scrub occupies the 

 slopes of the mountains, filling up the valleys so as to render them 

 impenetrable. Here the summer is short, the ground not being free 

 of snow till the middle of June. It is, however, comparatively dry, 

 and the Alpine flora very much resembles that of the Western 

 Himalaya and (in generic types at least) the Alps of Europe and 

 Western Asia ; while as we advance towards the Tibetan region we 

 have a great increase of dryness, so that a Siberian flora is rapidly 

 developed, which at last entirely supersedes that of the sub-Alpine 

 zone, and ascends above 18,000 feet." 



Sir J. D. Hooker's own collection of Sikhim plants amounted to 

 2,920 species, of which 150 were ferns. Assuming that he failed to 

 get 25 per cent, of the plants during his short residence, the total 

 of about 4,000 species of flowering plants and ferns together for 

 Sikhim will be arrived at, and be very near the real number. Owing 

 to the humid climate of Sikhim, and the absence of excessive cold 

 at any season of the year over the greater part of it, the prevailing 

 vegetation is of an evergreen character. A few trees, and two tree- 

 ferns growing at elevations under 6,000 feet, have the abnormal 

 habit of shedding their leaves and remaining bare during part of 

 the warmest and wettest seasons when their neighbours are making 

 their most vigorous growth ; whilst other trees, chiefly of higher 

 elevations, have the ordinary habit of shedding their leaves towards 

 the end of autumn and remaining bare till spring. The vast majo- 

 rity, however, of the Sikhim trees and shrubs are evergreen. As 

 might be expected from the dripping nature of the climate, ferns 

 are a predominating feature of the vegetation generally, but more 

 especially of that of the extra dripping and misty region lying 



