FTLICES ,85 



Principal genera : — Adiantum (L.), Cheilanthes (Sw.), Pellaea (Link), 

 Pteris (L.), Lomaria (Willd.), Blechnum (L.), Woodwardia(Sm.), Doodia 

 (R. Br.), Asplenium (L.), Scolopendrium (Sm.), Aspidium (Sw.), Nephro- 

 dium (Rich.), Lastrea (Presl), Nephrolepis (Sch.), Polypodium (L.), Notho- 

 clsena (R. Br.), Gymnogramme (Desv.), Hermonitis (L.), Vittaria (Sm.), 

 Acrostichum (L.), Platycerium (Desv.), Onoclea (L.), Woodsia (R. Br.), 

 Ceterach (Adaps,), Dicksonia (L'Herit.), Davallia (Sm.), Cystopteris 

 (Bernh.), Lindsaya (Dry.). 



Order 2. — Cyatheace^. 



This order is not distinguished from the Polypodiacese by any very 

 clear Hnes of demarcation. The sporanges are epidermal and shortly 

 stalked ; they have a complete oblique eccentric annulus. The sori 

 are seated on a receptacle or placenta which often projects consider- 

 ably ; they are naked, or are more often enclosed in 

 a cup-shaped indusium or ' involucre,' which some- 

 times forms a closed cup opening by a transverse 

 fissure ; the sporanges are densely crowded in the 

 sorus. The greater number of the tree-ferns 

 belong to this family (fig. 57). The leaves are 

 often very large (five to ten feet in length), and 

 usually compoundly pinnate, forming a rosette at the summit of the 

 columnar unbranched arborescent stem, which is densely covered 

 with aerial roots, especially in its lower portion, and is marked in a 

 diamond pattern by the scars of fallen leaves. In some species, in 

 addition to the ordinary cylinder of ' vascular ' bundles, there are a 

 number of accessory bundles distributed through tTie medulla and 

 cortex, forming a delicate open network. Crystals of calcium oxalate 

 are not uncommon in the epidermal cells. 



Principal genera : — Cyathea (Sm.), Hemitelia (Br.), Alsophila (R. Br.). 



Fig. 59. — Sorus of CyaM^ff, 

 with open indusium (mag. 

 niiied). 



Order 3. — Gleicheniace^. 



The sporanges are epidermal and sessile, with a 

 broad complete transverse annulus running nearly hori- 

 zontally, and hence with vertical dehiscence. The sori 

 are naked, on the under side of ordinary leaves, and 

 usually consist of only three or four sporanges. The 

 stem is a slender creeping rhizome ; the leaves are usually 

 very large, and with peculiar buds or ' innovations ' on 

 the lamina. 



Principal genera :— Gleichenia (Sm.), Mertensia (Willd.). 



Fig. 60, — Sporange 

 of Gleichenia 

 (magnified). 



