928
FILICES.
[Hymenophyllum.
| Indusium reniform and attached by the sinus. Fronds usually 2–4-pinnate; pinnæ not articulated to the rhachis | 20. Nephrodium. |
| Indusium reniform and attached by the sinus. Fronds pinnate; pinnæ articulated to the rhachis | 21. Nephrolepis. |
| ** Indusium altogether absent. | |
| Sori globose or broadly oblong, dorsal, distinct | 22. Polypodium. |
| Sori oblong or rounded, at first distinct but ultimately confluent, marginal, often partly concealed by the reflexed margin of the frond and then barely distinguishable from Cheilanthes | 23. Nothochlæna. |
| Sori oblong or linear, simple or forked, often confluent, dorsal | 24. Gymnogramme. |
| Suborder IV. Gleicheniaceæ. Sori dorsal, naked, of few (2–6) sporangia; receptacle not elevated. Sporangia sessile or nearly so, splitting vertically, surrounded by a complete transverse ring. | |
| Fronds dichotomously forked; ultimate branches pinnately divided | 25. Gleichenia. |
| Suborder V. Schizæaceæ. Sporangia crowded, not collected into distinct sori, sessile or nearly so, with a complete transverse ring just below the apex, splitting vertically. Fertile portions of the frond much modified. | |
| Fronds simple or forked or flabellately divided, without an expanded lamina. Sporangia in 2–4 rows on the under-surface of short linear fertile pinnæ terminating the fronds | 26. Schizæa. |
| Fronds very long, climbing; primary pinnæ dichotomously or pinnately divided. Sporangia in 2 rows on the under-surface of contracted fertile pinnules | 27. Lygodium. |
| Suborder VI. Osmundaceæ. Sori irregular, distinct or confluent, dorsal; indusium wanting. Sporangia sessile or nearly so, splitting vertically; ring rudimentary, placed just below the apex. | |
| Fronds opaque or translucent, 2–3-pinnate | 28. Todea. |
| Suborder VII. Marattiaceæ. Sori distinct, dorsal. Sporangia sessile, without any ring, coriaceous, splitting vertically or opening by a pore at the apex, usually cohering in concrete masses called synangia. | |
| Rhizome large, tuberous. Fronds large, 2–3-pinnate | 29. Marattia. |
| Suborder VIII. Ophioglossaceæ. Sporangia globose, coriaceous, sessile, without any ring, dehiscing by a transverse or vertical slit, crowded on a linear spike or on the branches of a panicle. Fronds not circinate in vernation. | |
| Sterile frond simple and entire. Sporangia on a linear spike | 30. Ophioglossum. |
| Sterile frond pinnate or 2–4-pinnate. Sporangia on the linear branches of a panicle | 31. Botrychium. |
1. HYMENOPHYLLUM, Linn.
Usually small and sometimes minute ferns. Rhizome slender, creeping, often much branched and matted. Fronds simple or more generally compound, delicately membranous, often pellucid, usually of a single layer of cells; segments entire or toothed at the margin,
