72 VASCULAR CRYPTOGAMS 



separated by long internodes. The ultimate roots are always adventi- 

 tious ; that is, there is no predominant axial root which is a prolongation 

 downwards of the main axis of the plant, as in many Dicotyledons and 

 some Monocotyledons. They are usually very numerous, especially in 

 tree-ferns, arising in acropetal succession, and completely clothing the 

 lower part of the stem, or, where this is supj^ressed, the leaf-stalks, as in 

 the case of the common ' male fern ' (Aspidium filix-mas, Sw.). The 

 ultimate branches of the root are furnished with a root-cap as in Flower- 

 ing Plants. The leaves, or, as they are more commonly called, ' fronds,' 

 are invariably stalked, and are remarkable in many species, especially 

 when they attain a large size, for the great extent to which subdivision 

 of the lamina is carried ; in some tree-ferns they attain a length of from 

 six to ten feet. In the filmy ferns they consist, as in Muscinese, of only 

 a single layer of cells penetrated by distinct ' vascular' bundles. Stomates, 

 similar in structure to those of Flowering Plants, occur abundantly both 

 on the under side of the leaf and on the leaf-stalk, except in the 

 Hymenophyllaceae. The leaves exhibit very little metamorphosis com- 

 pared to those of Flowering Plants. Most usually all the leaves are alike 

 in form and extent of division, and even nearly so in size ; but in some 

 species only certain of the leaves, sporophylls, are fertile, and these then 

 show a more or less well-marked difference from the barren leaves, as in 

 our 'hard fern ' (Lomaria spicant, Desv.)and 'parsley fern '(Cr^-ptogramme 

 crispa, R. Br.). In the ' elk's-horn fern ' (Platycerium alcicorne, Desv.), 

 commonly grown in cultivation, the leaves are alternately broad thallus- 

 like barren plates, closely applied to the surface on which the plant 

 grows, and long erect dichotomously branched fertile leaves. The 

 leaves (except the first, which spring from the prothallium) are circinate 

 in vernation, both the principal rachis and the midrib of the pinnae 

 (when the leaf is pinnate) being rolled up on their upper side — owing to 

 the more rapid growth of the cells on the under than those on the upper 

 surface — and only slowly unroll as the development of the leaf advances. 

 The young leaves, and the rachis and petiole of mature leaves, are 

 generally more or less completely clothed with pales or ramenta, flat 

 brown scale-like trichomes or outgrowths of the epiderm. These are 

 often glandular, and sometimes contain crystals of oxalate of lime. They 

 serve as a protective mantle to the young stem and leaves, and also as a 

 reservoir of moisture. Capitate, glandular, and other more ordinary 

 kinds of hair are also of frequent occurrence. In the typical ferns the 

 sporanges are also trichomic in their origin. They are collected into 

 groups or sori (fig. 58), usually formed in connection with a 'vascular' 

 bundle. In unilamellar leaves these sori are placed on the edge, in all 

 others almost invariably on the under side of the leaf, especially of its 



