FILICES 



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 (Adans.), Dicksonia (L'Herit.), Davallia (Sm.), Cystopteris 

 (Bernh.), Lindsaya (Dry.). 



with open indusium (mag- 



ORDER 2. CYATHEACE^E. 



This order is not distinguished from the Polypodiaceae by any very 

 clear lines 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 the 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.). 



ORDER 3. GLEICHENIACE^E. 



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 : Gieichenia (Sm.), Mertensia (Willd.). 



, 



FIG. 60. Sporan^e 



of Gieichenia 

 (mas " ified >' 



