CHAEACTBES OP TEIBES AND GENERA. 253 



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

 dad, it is peculiar for liaTing 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 g-enus 

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

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

 true Alsopldla. The evidence of its being- a tree Fern rests 

 entirely on Wildenow's description, which says " caudex 

 erectus arboreous," but s.ccording- to a plant at Kew, which 

 in 186i had fronds 2 to 3 feet hig-h, the caudex was decum- 

 Ijeut, bat 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 LopJiosoria in PJicjopleris. 



S-p. A. blechnoides, Klot. in Linn. {Metaxya rostratum, 

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

 sophila hlecJinoides, Hook. Sp. Fil.) 



]Sr(jTB. — In the preceding- tribes the sori are discal ; and 

 marg-inal in the six followina-. 



Trihe ] 6.— DICKSONIE^. (Plate IC.) 



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 

 marg-in of the frond, the two forming- an urceolate, bi- 

 valved, marginal cyst, containing- the sporangia. 



Obs. — Hitherto I included under this tribe the g-enera 

 Sitoholium, Lindscea, Microlepia, and other allied g-enera, 

 which, although agreeing in the technical character of 

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



