Changes as remarkable take place in the sori of the Asplenium lanceolatum. At first, when the sori are covered by their white indusium, they are oblong, but they become circular as they enlarge, and eventually often confluent, so as to form a line round the whole under-margin of the sharply toothed pinnule. This fern, which is indigenous in the Atlantic islands, and is found in the Channel Islands, as well as in the maritime counties of England and Wales, grows in the crevices of rocks and old walls, or clothes the sides of wells and deserted mines. It belongs to the section which has a mid-vein. The genus Ceterach apparently belongs to that section of ferns which have a vertical ring, and no indusium; but its affinities ally it closely with Asplenium. Its want of an indusium is supplied, perhaps occasioned, by the abundance of chaffy scales which cover the back of the fronds. The lateral veins are alternate and irregularly branched, with the branches anastomosing towards the margin. The sori are oblong or linear, attached to the upper side of the anterior branches except the last, which is on the opposite side of the lower branch. The British species, Ceterach officinarum, or Scaly Spleen-wort (fig. 64), has deeply pinnatifid, lanceolate fronds, with oblong, obtuse, alternate segments, and linear sori. The whole of the under-surface is densely clothed with brown, pointed, imbricated scales, finely serrated at their margins, the outermost of which extend beyond the edges of the segments. They completely cover the sori, and at first hide them entirely from view. On the unexpanded fronds, the scales are white and silvery. ‘This plant has an obscure indusium, only perceptible at an early stage of fructification, and subsequently as a nearly erect membrane, attached to the back of the vein. It is rendered unnecessary by the arrangement of the scales, which are disposed in regular series along each side of the veins and veinlets, pointing outwards, and concealing the sori with their broad bases, which completely overlap them in their immature condition.’ [Illustration: Fig. 64. Ceterach officinarum.]