508 FILICES. 



Iu 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 (antheridia) contain sperm-cells (sperma- 

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

 (archegonia) contain a solitary free germ-cell. The antherozoids find then- 

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

 develops into a plant, the prothallus withering away. 



Tribe I. HYMENOPHYLLEffi. 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. 



Tribe II. POLYPODIE'JE. 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. 



* Son 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. "VVoodsia. 



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. Gymnogramme. 



Tribe III. OSMUN'DEJE. 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'SEiE. Capsules large, 2-valved, without a ring 

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



Frond ovate, simple. Capsules spiked 16. Ophioglossum . 



Frond pinnate. Capsules panicled 17. Botrychium. 



