VEGETATION. 83 



between 5,000 and 9,000 feet, where they are to be seen on every rock, 

 on the stems of trees, and growing on the ground. Mr. C. B. Clarke, 

 in his valuable paper on the Ferns of Northern India, published in 

 the Linnean Society's Journal for 1879, enumerates eight species of 

 tree-ferns and 248 of stemless and sub-arborescent sorts found between 

 Nepal and Assam. Probably over 200 of them are indigenous to 

 Independent Sikhim. There are, besides, several species of Lyco- 

 podium and Selaginella, which are usually associated with the true ferns. 

 Above 5,000 feet the European club-moss {Lycopodium clavatum) is in 

 great abundance and luxuriance on the ground and rocks in open 

 spaces, and several handsome tasselled species of the same genus 

 are pendent on the limbs of trees. Of the eight species of Sikhim 

 tree-ferns noted by Clarke, five are found between the lowest levels 

 and 4,000 feet, and three between 3,500 and 7,000 feet. They are 

 all most graceful objects and form a striking feature in the landscape 

 wherever they occur, but more especially so in the moister, unculti- 

 vated valleys, where, undisturbed, they attain their full luxuriance, 

 and are found either as isolated individuals, in small groups, or in 

 extensive groves. Their average height is about twenty feet, but 

 plants of forty and fifty feet are not very uncommon. The eight 

 species are included in two genera, viz., two in the genus Hemitelia 

 and six in Alsophila. The sori are placed on cup-shaped receptacles 

 in the former, whilst in the latter they are exinvolucrate as in Poly- 

 podium, from which the genus Alsophila is separated more on account of 

 the gigantic size of its component species than by any very definite 

 character. Semitelia decipiens ranges from low elevations to 4,000 

 feet, where it is replaced by its congener S. Brumniana, which 

 ascends to 7,000 feet, the limit of tree-fern vegetation in Sikhim. 

 Both the Hemitelias, but especially decipiens, have stipes densely 

 armed with short, stout wrickles. For ready identification the A Isophilas 

 may be divided into two groups ; one comprising the species with 

 single or rarely once-forked stems, and the other those with many- 

 branched stems bearing numerous heads of fronds at different heights 

 on the same plant. To the first group belong A. glauea, which grows 

 at elevations under 4,000 feet, and is distinguished by the bluish-hue 

 of its stipes and grayish under-surface of the fronds, and A. latebrosa, 

 closely resembling Hemitelia Bnmoniana, and with the same distri- 

 bution, but distinguished by its exinvolucrate sori. The species falling 

 into the second group are A. glabra, the most tropical of the tree-ferns, 

 recognized by the V-shaped arrangement of the sori ; A. Andcrsoni, 

 growing generally in dense shade by banks of streams below e3,500 

 feet, resembles A. glabra in growth, but is of a dull dark green colour, 

 and its sori are in almost parallel lines ; and A. Oldhami and A. ornaia, 

 both of the upper forests lying between 4,500 and 6,000 feet. 



