CHARACTERS OF TRIBES AND GENERA. 253 



of many localities in tropical America, also found in Trini- 

 dad, it is peculiar for having- two or more sori on some of 

 the branches of the veins. Being arborescent, and the sori 

 criniferous, has led several authors to refer it to the genus 

 Alsophila, but from which it differs in the vernation (base of 

 the stipes), being criniferous, which is not the case with 

 true Alsopliila. The evidence of its being a tree Fern rests 

 entirely on Wildenow's description, which says "caudex 

 erectus arboreous," but according to a plant at Kew, which 

 in 1864 had fronds 2 to 3 feet high, the caudex was decum- 

 bent, but which probably only required time to assume an 

 arboreous character ; whichever it may be, I find it difficult 

 to point out its relationship with any sequence of genera, 

 except that it may be ranked with Lophosoria in Phegopteris. 



Sp. A. blechnoides, Klot. in Linn. (Metaxya rostratum. 

 Hook, and Bauer. ; P. ParJceri, Hook, and Grev., t. 232 ; Al- 

 sopliila blechnoides, Hook. Sp.'Fil.) 



NOTE. In the preceding tribes the sori are discal ; and 

 marginal in the six following. 



Tribe 16. DICKSONIE^J. (Plate 16.) 



Vernation fasciculate, decumbent or erect, and* becoming 

 arborescent. Sori marginal, globose, or transverse ob- 

 long, furnished with an interior attached special indusium, 

 which connives more or less with the changed indusioid 

 margin of the frond, the two forming an urceolate, bi- 

 valved, marginal cyst, containing the sporangia. 



OBS. Hitherto I included under this tribe the genera 

 Sitobolium, Lindscea, Microlepia, and other allied genera, 

 which, although agreeing in the technical character of 

 their sori, nevertheless differ widely in habit, so much so, 



