78 VASCULAR CRYPTOGAMS 



with remarkable stolons, the extremities of which swell up into tubers ; 

 but it is uncertain whether they belong to the stem or the root. In 

 other cases adventitious leaf-buds are borne on the upper surface of the 

 lamina or in the axils of the leaves. In Woodwardia radicans (Sm.) and 

 some other species, the long drooping leaves may root in the soil and 

 put up new shoots. The veins in the leaves of the great majority of 

 ferns do not anastomose, but divide repeatedly dichotomously. Their 

 ' vascular ' bundles differ, in some cases, from those of the stem in being 

 collateral, the xylem facing the upper, the phloem the under surface of 

 the leaf. 



With the exception of some species of Trichomanes, all ferns have 

 true roots, characterised, like those of Vascular Cryptogams generally, 

 and of Flowering Plants, by the presence of a true root-cap, composed of 

 several layers of cells, and by the tendency of the epidermal cells to 

 develop into long unsegrnented filaments or root-hairs, by which the 

 nutriment is absorbed from the soil. These proceed in acropetal suc- 

 cession from the creeping underground stem or rhizome, or, where the 

 stem is erect, ver}- short, and densely covered with leaves, from the leaf- 

 stalks. In tree-ferns the lower part of the erect stem is densely covered 

 with a thick felt-like envelope of slender roots, which give a broad base 

 to the stem. Like the stem, the tissue of the root develops from a 

 single apical cell. The branching is always monopodial. The lateral 

 rootlets arise in acropetal succession on the outside of the primary 

 ' vascular ' bundle. The root is traversed by a single axial cylinder 

 formed by the coalescence of ' vascular ' bundles. 



The epiderm of the leaves of those ferns which are not unilamellar 

 differs in no essential respect from that of Flowering Plants, but its cells 

 contain a larger quantity of chlorophyll. The epiderm of the under 

 side only is abundantly provided with stomates, which are usually of 

 quite the ordinary structure. In some cases, as Aneimia (Sw.), they 

 present the peculiar appearance of the two guard-cells being entirely 

 enclosed within a single epidermal cell. Those of Kaulfussia (Bl.) 

 (^Nlarattiacese) are ver}^ large, and of peculiar structure. 



The sporanges of ferns are rounded, ovoid, or pear-shaped capsules, 

 seated on long stalks in the Polypodiaceae and Cyatheaceae, sessile in 

 the other orders. When mature, the wall of the capsule consists, 

 except in the Marattiace^e, of a single layer of cells, a particular row of 

 which, running longitudinally, transversely, or obliquely round the 

 capsule, usually undergoes special development, and is known as the 

 annulus ; but the annulus may be entirely wanting, as in the ]\Iarat- 

 tiaceae, or its place may be taken by the special development of an 

 apical or lateral group of cells, as in the Osmundace^. Where there is 



