To the Asplenieæ proper belongs one of our commonest species, the Athyrium Filix-fœmina, or Lady Fern, which, when growing in moist shady places, is one of the most elegant of British ferns. Its bipinnate frond varies from a broad almost ovate outline to a linear lanceolate form. The numerous fronds often spring from the caudex in a vase-like arrangement, to the height of four or five feet, those in the centre nearly erect, but the outer ones, drooping around in all directions, forming a tuft of lovely feathery foliage. The sori have commonly a semilunar outline, as in fig. 62; but they are occasionally so much curved as to acquire a horse-shoe form, and more rarely they are linear, and they become at length reflected by the growth of the sporangia. In some varieties they are distinct, in others so close as to become eventually confluent and completely cover the surface. The Filix-fœmina is distinguished by the linear junction of the indusium with the frond. It is one of the most variable of all the known ferns, and is remarkably prolific, so that new forms may be raised from the spores. There are a very large number found in this country. [Illustration: Fig. 62. Athyrium Filix-fœmina.] All the Asplenieæ have linear sori attached to the side of the vein, so that they are said to be lateral. The indusium opens on its inward side, and is sometimes ciliated. There are many tropical ferns of this group, but the genus Asplenium, which has representatives in all parts of the world, yields eight or nine species in Great Britain. [Illustration: Fig. 63. Asplenium Ruta-muraria.] The Asplenium Ruta-muraria, or Wall Rue, is an indigenous mountain plant growing in tufts six or eight inches high in the clefts of the rocks, but has diminished much in size in migrating to the plains, where it is found on old brick walls and outhouses. The fronds are deltoid and bipinnate, the pinnules are wedge-shaped and notched, or toothed, on their upper margin; their colour is deep green, but in exposed situations they are always covered with a glaucous secretion. The veins diverge from the footstalk at the base of the pinnules, branch out above, and extend to the teeth or serratures, as in fig. 63. The sori, which are produced on the inner side of the veins, are linear, elongated, and eventually become confluent, covering the whole under-surface of each fertile pinnule. The indusium, which is only traceable in the earlier condition of the fructification, is white, and the free inner margin is somewhat jagged.