[Illustration: THE BITING STONECROP OR WALL PEPPER.] We have now to consider a few species of the order _Crassulaceæ_, which includes some very interesting succulent plants that are peculiarly adapted to a life in the dryest of situations on walls, roofs, &c. In addition to the thick, fleshy nature of their stems and leaves, these plants are distinguished by terminal cymes or corymbs of flowers with (usually) five sepals, the same number of distinct petals, twice as many stamens arranged in two whorls, and carpels equal in number to the petals. Three of the plants referred to are known as Stonecrops, and may be recognised by the following descriptions:-- 1. The English Stonecrop (_Sedum anglicum_).--A smooth plant, two or three inches high, abundant in rocky and stony places, especially in the West and near the sea, flowering from June to August. Its stems are more or less decumbent, much branched and rooting at the base; and its leaves are small, thick, almost globular, of a pale green colour with, often, a tinge of red. On the small flowerless branches the leaves are very crowded and overlapping; but on the taller, flowering stems they are more scattered and placed alternately. The little starlike flowers are white, frequently tinged with pink or spotted with red, and arranged in a short, two-forked panicle. They have short, green sepals; narrow, sharply-pointed petals about twice the length; and stamens with bright red anthers. [Illustration: THE WALL PENNYWORT OR NAVELWORT.] 2. The White Stonecrop (_S. album_).--A somewhat similar plant, from three to seven inches high, sometimes seen in large clusters on rocks, walls, and roofs, bearing white or pinkish flowers during July and August. The whole plant is smooth; and its short creeping stock gives rise to short barren stems with crowded leaves, and erect flowering stems with scattered leaves. The leaves are very thick, of a bright green colour, about a third of an inch long, and oblong or cylindrical in form. The panicles are much branched, with, usually, reddish stems; and each consists of numerous flowers with short, blunt sepals, and narrow, oblong petals about three times as long. This species is not so common as either the last or the following. 3. The Biting Stonecrop or Wall Pepper (_S. acre_).--A smooth plant, of a yellowish green colour, biting to the taste, very common on rocks, walls and roofs, bearing golden yellow flowers during July and August. It has short, barren stems, covered with closely-overlapping leaves arranged in six rows; and erect flowering branches from two to four inches in height. The leaves are very small, thick, succulent, oval or almost globular in form. The flowers, which are in small, terminal, three-cleft panicles, have very short, blunt sepals; and much longer, narrow, pointed petals.