508 FILICES. 



In germination the spore develops a flat cellular scale (prothallus), on the 

 under surface of which are formed cavities some containing male and some 

 female organs. The male cavities (antkeridia) contain sperm-cells (sperma- 

 tozoids or anther ozoids), which enclose a spiral filament. The female cavities 

 (archeyonia) contain a solitary free yerm-cM. The antherozoids find their 

 way into the archegoaia and fertilize the germ-cell, which thereupon 

 develops into a plant, the prothallus withering away. 



TRIBE I. HYMENOPHYIi'IiE.7E. Frond very membranous, translucent, 

 reticulate. Involucre 2-valved, urceolate or 2-lipped. Capsules minute, 

 membranous, reticulate, sessile on a clavate or filiform receptacle, girt by 

 a complete horizontal or oblique ring. Vernation circinate. 



Involucre 2-valved 1. Hymenophyllum. 



Involucre urceolate 2. Trichomanes. 



T.RIBE II. POIiYPODIE'-ffi. Frond more or less coriaceous, opaque. 

 Involucre marginal or dorsal or 0. Capsules minute, membranous, reticu- 

 late, not raised on an elevated receptacle, stalked, partially girt by a 

 vertical ring, bursting transversely. Vernation circinate. 



* Sori marginal ; involucre continuous with the reflexed or recurved margin 

 of the frond. 



Sori oblong, short. Fronds all similar 3. Adiautum. 



Sori linear, continuous. Fronds all similar -.4. Pteris. 



Sori subglobose, on special fronds 5. Cryptogramme. 



Sori linear, on special fronds 6. Lomaria. 



** Sori dorsal, linear ; involucre linear. 



Involucre on a nerve, single 7. Asplenium. 



Involucre on a nerve, double 8. Scolopendrium. 



*** Sori dorsal, globose ; involucre short. 



Involucre lacerate, attached under the sorus 9. "Woodsia. 



Involucre hooded, on one side of the sorus 10. Cystopteris. 



Involucre orbicular, peltate 11. Aspidium. 



Involucre reniform 12. Nephrodium. 



**** 



Sori dorsal ; involucre (see Ceterach under Asplenium). 



Sori globose or oblong 13. Polypodium. 



Sori linear 14. G-ynmograrnme. 



TRIBE III. OSMUN'DE.ffi. Frond coriaceous or membranous. Involucre 

 0. Capsules sessile or shortly stalked, vertically 2-valved, with a short 

 lateral or subterminal striate areola. Vernation circinate... 15. Osmunda. 



TRIBE IV. OPHIOGLOS SE.JE. Capsules large, 2-valved, without a ring 

 or areola, coriaceous, in spikes or panicles. Vernation straight. 



Frond ovate, simple. Capsules spiked 16. Ophioglossum. 



Frond pinnate. Capsules panicled 17. Botrychium. 



