The Aspidieæ form an extensive and widely distributed group, embracing several of our common British species. One of these is the genus Lastrea, which has, for the most part, lanceolate fronds, bipinnate or tripinnate in division, with linear lanceolate, and usually pinnatifid pinnæ. The sori are nearly circular, seated upon the back of the veins, and covered by a reniform indusium, which is attached by its sinus. In Lastrea Filix-mas (fig. 57), one of our commonest ferns, the fronds spring up in a rather spreading mass, from the extremity of a long scaly caudex, and often present a vase-like tuft hollow in the centre. The rachis, leafy through a third or a fourth of its length, is more or less clothed with thin membranaceous scales, of a pale often brownish-golden hue, a peculiarity common to the other Lastreæ. Lastrea Thelypteris, the Marsh Fern, however, has them not, and differs also from most of its congeners in having its sori submarginal. Its rhizome has a widely creeping habit of growth. The Lastrea æmula has globular glands, sessile over the whole under-surface of the fronds, which secrete a perfume like new-made hay. From a similar cause, Lastrea rigida was botanically known as Polypodium fragrans. This coumarine odour is possessed by several other ferns, notably by Cheilanthes odora. The Oleandra, which is a foreign genus, has simple fronds articulated near to the rhizome, and its sori are placed on the tips of the parallel veinlets. The Oleandra neriiformis, which grows on open spots, has an erect rhizome, and assumes quite a shrubby habit, rising to from four to six feet, and bearing at intervals whorls of fronds. [Illustration: Fig. 58. Sorus and Indusium of Polystichum or Aspidium.]