Hymenophyllaceaey Polypodiaceae 5 



strand horseshoe-shaped in cross section. Sporangia 

 massive, shortly stalked with vertical dehiscence, not 

 arranged in sori, but thickly set on the surface of 

 special, often reduced, fronds or pinnae. 



Only British genus : Osmunda. 



Gradatae (Bower). Sporangia basipetal, on a more 

 or less elongated receptacle, of moderate size, shortly 

 stalked, with medium spore output. Annidiis oblique. 

 Indushtm a basal cup, entire or 2-lipped. 



Family Hymenophyllaceae. Rhizomes creeping, 

 haplostelic, bearing fronds with thin filmy laminae which 

 have no stomata or intercellular spaces in the mesophyll. 

 Sori marginal on the ends of excurrent veins. 



Prothalli filiform. Indusium tubular. Trichomanes. 



Prothalli flat. Indusium 2-lipped. 



Hymenophyllum. 



MiXTAE (Bower). Sporangia of various ages mixed 

 without regular orientation, grouped in sori^ on flat or 

 nearly flat receptacles, more rarely scattered over the 

 leaf, typically small, with thin elongated stalks and 

 with small spore output. Annulus vertical, incomplete, 

 dehiscence transverse. Indtisitmi various or absent. 



Family POLYPODIACEAE. Rhizome of various habit, 

 typically dictyostelic. 



Tribe i. Woodsieae. Sort globose, often sub- 

 marginal. Indusinni cup-shaped, opening laterally or 

 splitting irregularly. Spores bilateral. 



Indusium often ciliate, attached basally. Woodsia. 



Indusium hooded, attached laterally. Cystopteris. 



