372 PART IV. CLASSIFICATION. 



Ceterach, may be included here, though the indusium may be rudimen- 

 tary or absent. 



(c) Aspidiect'. Sorus on the lower surface of the leaf, orbicular in form 

 and covered \>y a peltate or reniform superior (Fig. 214 _D) or inferior 

 indusium. Nephr odium (Lastrcea) Filix mas, the male Fern, and other 

 species resembling it, with a thick tufted crown of leaves, are not rare in 

 woods. Aspidium is the Shield-Fern : A. (Polystichum) Lonchitis is the 

 Holly-Fern : "Woodsia, Onoslea, and Cystopteris (Bladder-Fern), with an 

 inferior indusium, also belong to this group. 



(d) Polypodies. The sorus, which is on the under surface of the leaf, is 

 naked (Fig. 214 F). In the section Polypodium the leaves are articulated 

 to the stem, so that when they die and fall off they leave a roundish scar ; 

 the leaves are usually borne in two rows on the dorsal surface of the 

 rhizome. Polypodium vulgare, with simple pinnate leaves, is common on 

 tree-trunks, rocks, etc. In the section Phegopteris the leaves are not 

 articulated to the stem, so that when they die, fragments of the leaf -stalks 

 remain attached to it : Cryplogramme crispa is the Parsley-Fern : Pliegop- 

 tsris Dryopteris and polypodioides are the Oak- and Beech-Ferns. 



Order 3. Cyatheaceae. Distinguished from the Polypodiaceae only by 

 the presence of a complete annulus. 



The Tree-Ferns belong to this family. Cibotium and Dicksonia have 

 marginal sori with two-valved inferior indusia : Cyathea, Hemitelia, and 

 Alsophila have their sori on the under surface of the leaf : Alsophila alone 

 has no indusium; in Cyathea it is cup-shaped, and in Hemitelia one- 

 valved. 



Order 4. Gleicheniaceae, including the genus Gleichenia with a hori- 

 zontal annulus ; no indusium : all tropical. 



Order 5. Schizaeaceae, including the genera Schizaea Aneimia, Mohria 

 and Lygodium, with a projecting apical annulus to the almost sessile 

 sporangium, occur only in the tropics. Lygodium is the most remarkable 

 genus ; its pinnate leaves grow to a great length, and twine round supports 

 by means of their midribs : it alone has an indusium, and the sorus is 

 usually unisporangiate. 



Order 6. Osmundaceae. The shortly-stalked sporangia have a rudi- 

 mentary annulus consisting of a group of cells just below the apex; they 

 burst open by a longitudinal slit on the side opposite to this. 



Osmunda re/jails, the Fern-Royal, is a not very common but well-known 

 Forn. Only the upper pinnae of the leaves are fertile, and develope little or 

 110 mesophyll ; the sori are marginal, and consist of a great number of 

 sporangia; they have no indusium. The only other genus is Todea, 

 belonging mainly to Australasia. 



