On the following day we marched to Yoksun: the weather was fair, though it was evidently snowing on the mountains above. I halted at the Ratong river, at the foot of Mon Lepcha, where I found its elevation to be 7,150 feet; its edges were frozen, and the temperature of the water 36°; it is here a furious torrent flowing between gneiss rocks which dip south-south-east, and is flanked by flat-topped beds of boulders, gravel and sand, twelve to fourteen feet thick. Its vegetation resembles that of Dorjiling, but is more alpine, owing no doubt to the proximity of Kinchinjunga. The magnificent _Rhododendron argenteum_ was growing on its banks. On the other hand, I was surprised to see a beautiful fern (a _Trichomanes,_ very like the Irish one) which is not found at Dorjiling. The same day, at about the same elevation, I gathered sixty species of fern, many of very tropical forms.[114] No doubt the range of such genera is extended in proportion to the extreme damp and equable climate, here, as about Dorjiling. Tree-ferns are however absent, and neither plantains, epiphytical _Orchideæ,_ nor palms, are so abundant, or ascend so high as on the outer ranges. About Yoksun itself, which occupies a very warm sheltered flat, many tropical genera occur, such as tall bamboos of two kinds, grasses allied to the sugar-cane, scarlet _Erythrina,_ and various _Araliaceæ,_ amongst which was one species whose pith was of so curious a structure, that I had no hesitation in considering the then unknown Chinese substance called rice-paper to belong to a closely allied plant.[115] [114] They consisted of the above-mentioned _Trichomanes,_ three _Hymenophyllæ, Vittaria, Pleopeltis,_ and _Marattia,_ together with several _Selaginellas._ [115] The Chinese rice-paper has long been known to be cut from cylinders of pith which has always a central hollow chamber, divided into compartments by septa or excessively thin plates. It is only within the last few months that my supposition has been confirmed, by my father’s receiving from China, after many years of correspondence, specimens of the rice-paper plant itself, which very closely resemble, in botanical characters, as well as in outward appearance of size and habit, the Sikkim plant. The natives collect the leaves of many Aralias as fodder for cattle, for which purpose they are of the greatest service in a country where grass for pasture is so scarce; this is the more remarkable, since they belong to the natural family of ivy, which is usually poisonous; the use of this food, however, gives a peculiar taste to the butter. In other parts of Sikkim, fig-leaves are used for the same purpose, and branches of a bird-cherry (_Prunus_), a plant also of a very poisonous family, abounding in prussic acid.