CHARACTERS OP TRIBES AND GENERA. 315 



OBS. This genus is founded on a remarkable Fern, a 

 native of Brazil, New Granada, and other parts of Tropical 

 America, climbing to the tops of lofty trees, similar to the 

 genus Lygodium. In the character of its fructification it 

 does not differ much from Blechnum, but has the veins 

 combined at the margin, and, with the peculiar nature of 

 the indusium, which continues long permanent, and even 

 enlarges in size after it has become reflexed, is sufficient to 

 mark this as a genus distinct from Blechnum. 



Sp. S. volubile, J. Sm. (v v.) (Hook. Gard. Ferns, t. 15). 



Tribe 23. ASPLENIE^E. (Plate 23). 



Sori oblong or linear, oblique to the mid-rib or axis of 

 venation. Sporangia produced on one side (unilateral) or on 

 both sides of the same venule (bilateral), each furnished 

 with a plane or vaulted lateral operculiform linear indu- 

 sium, opening interiorly or exteriorly. 



OBS. In the " Species Filicum" 307 species are described 

 as belonging to this Tribe, but which in the " Synopsis" of 

 that work are reduced to 282 ; but in the Appendix to the 

 second edition 50 additional are recorded. They are found 

 in all regions of the earth favourable to Fern life, some 

 growing on cliffs or rocks, exposed to the extremes of heat 

 and cold, others in shady ravines or caves, others on the 

 ground or on trees, presenting great variation in the size 

 and form of their fronds, which are generally fasciculate 

 or rarely uniserial, the axis of vernation being generally 

 acaulose, a few becoming subarborescent. The numerous 

 intermediate forms render it most difficult to arrive at any 

 satisfactory conclusion as to the number of distinct species. 

 In Moore's "Index Filicum" Asplenium occupies 70 pages, 



