254 



over the whole under surface (and occasionally the upper) except on the 

 rachis and costae ; sporangia stalked, compressed, girdled by a vertical 

 jointed band, splitting when ripe transversely ; usually naked and des- 

 titute of any involucral covering. 



This tribe as here viewed, and represented in this Flora, comprises 

 only a single large genus, in which regardless of diversity of habit, ve- 

 nation and circumscription — which characters authors have adopted 

 for dividing it into several genera — are included all those plants which 

 have naked amorphous sori, and though confessedly an heterogeneous 

 assemblage, the character is an obvious and easily recognised one. 

 They are principally tropical subjects, and have their head-quarters 

 on the islands and mainland of equatorial America, where about two- 

 thirds of the known species exist. 



Genus XXXY, Acrostichum, Linn. 



Sori diffused in a uniformly even superficial layer over the under, 

 and in a few cases the upper surface of the frond ; sterile and fertile 

 fronds (except in one case) distinct, the latter usually more or less con- 

 tracted; venation free or variously anastomosing ; habit and circumscrip- 

 tion various. 



This well marked genus embraces about 200 species, the majority of 

 which are epiphytal subjects, living among moss and vegetable 

 debris on trees, rocks and decaying logs in damp forests; and of 

 the rest, the majority lift themselves clear of the ground where they 

 begin their growth, and ascend the nearest vertical surface by means 

 of their creeping or scandent rhizomes; so that very few are strictly 

 terrestrial. The barren fronds are permanent, usually for years, but 

 the fertile, which are produced only in season, and are herbaceous or 

 membranous in substance, mature and parish in a few weeks. Some 

 species only fruit during a limited portion of the year, generally in the 

 late summer months. 



Fronds simple. 

 Veins free. 



Fronds nearly or quite naked. 

 Fronds tapering at the base. 



Stipites of barren fronds usually under 1-2 in. 1. 



1. A. Herminieri, Bory. 

 Stipites of barren fronds usually over 2 in. 1. 



2. A. gramineum, Jenm. 



3. A. simplex, Swartz. 



4. A. inaDqualifolium, Jenm. 



5. A. alatum, Fee. 



6. A. viridifolium, Jenm. 



7. A. chart aceum, Baker. 



Fronds s! ortly tapering, cuneate or rounded at the base. 

 Stipites over 2 in. L 



8. A. pallidum, Baker. 



9. A. conform e, Swartz. 

 10 A. latifolium, Swartz. 



