GROUP III. PTERIDOPHYTA : FILICIN^ ; LEPTOSPORANGIATJ 1 ,. 405 



indusium present or absent. Almost all our native Ferns belong to this order, 

 which is exceptionally rich in genera. 



The following families may be distinguished, characterised by the position oi 

 the sorus. 



(a) Davalliea. Sorus marginal, or nearly so ; inferior indusium cup-shaped 

 in Eudavallia, or one-valved as in Leucostegia, etc. (Fig. 257 B). Includes the 

 large genus Davallia : no European species. 



(b) Pteridete. Sori coalescent along the margin of the leaf (Fig. 257 C), with 

 a spurious indusium. Pteris (Pteridium) aquilina, the Bracken, has a stem 

 which grows at some depth below the surface of the soil, and throws up every year 

 a single large, much-segmented leaf (frond) : it has also a true lateral indusium. 

 Adiantum, the Maiden-hair Fern, belongs to this group, as also Cheilanthes. 



(c) Aspleniece. The sorus, which is situated on the under surface of the leaf, 

 is elongated or linear, and the lateral indusium springs from the vein to which it 

 is attached (Fig. 257 E). Asplenium Ruta muraria, the Wall-Rue, is not uncom- 

 mon on walls and rocks ; A. Trichomanes is also abundant, with simple pinnate 

 leaves and a shining black rachis. Athyrium Filix fcemina, the Lady Fern, is 

 common in damp woods. Scolopendrium vulgare, the Hart's-tongue, with entire 

 leaves, is common in damp hedgerows and woods. Blechnum (Lomaria), the 

 Hard Fern, as also Ceterach, may be included here, though the indusium may 

 be rudimentary or absent. 



(d) Aspidiece. Soros on the lower surface of the leaf, orbicular in form and 

 covered by a peltate or reniform superior (Fig. 257 D) or inferior indusium. 

 Nephrodium (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) Lone hit is is the Holly Fern : Woodsia, Onoclea, 

 and Cystopteris (Bladder Fern), with an inferior indusium, also belong to this 

 group. 



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

 naked (Fig. 257 Fj. 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 iu two rows on the dorsal surface of the rhizome. Polypodiurn 

 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. Allosorus (Crypto- 

 gi-amme) crispu* is the Parsley Fern. 



(/) Acrostichi'te. The whole underside of the leaf is covered with naked 

 sporangia. To this family belong a number of tropical Ferns of the two 

 genera Platycerium and Acrostichum with its numerous sub-genera, Polybotrya, 

 Olfersia, Elaphpglossum, etc. 



Order 3. Cyatheaceae. Distinguished from the Polypodiaceae only by the 

 presence of a complete annulus. 



The Tree-Ferns belong to this family. Cibotium and Dicksoniahave 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 horizontal 

 annulus ; no indutium : all tropical. 



