The same order (_Crassulaceæ_) includes the House Leek (_Sempervivum tectorum_)--a plant which has been introduced into Britain, and is now commonly seen growing wild on rocks and on the roofs of country houses. Its spreading offsets give rise to globular tufts of flowerless shoots, and to thick, succulent, flowering stems that grow to a foot or more in height. The lower leaves are ovate, acute, thick, fleshy, edged with red, and arranged in a dense rosette; and the flowering stem, with its sessile leaves, is covered with a short, sticky down. The flowers are of a dull pink or purple colour, and are sessile along the spreading branches of the stem. They have usually about twelve short sepals; the same number of pointed petals, two or three times the length of the sepals; about twice as many stamens; and an ovary of as many carpels as there are petals and sepals. It is interesting to note that half the stamens--those forming the inner whorl--produce no pollen, and that their anthers are often modified into ovaries, the ovules of which, however, do not mature. This plant flowers in July and August. [Illustration: THE LONDON PRIDE OR ST. PATRICK'S CABBAGE.] Our last selection from this order is the Wall Pennywort or Navelwort (_Cotyledon umbilicus_)--a peculiar plant, common on rocks and walls in the South and West of England. It has a hard stock, producing an abundance of fleshy leaves early in the year, and flowering stems, from six to eighteen inches high, from June to August. The lower leaves are round, wavy, smooth, very succulent and brittle, and depressed in the centre where the long fleshy stalks are attached. Those of the stem have shorter stalks which are more and more removed from the centre from below upwards. The stem is thick and succulent, and bears a long raceme of pendulous yellow-green flowers on short stalks. Each flower has a very small calyx of five sepals; a cylindrical corolla, about a quarter of an inch long, with five short teeth; ten stamens, attached to the tube of the corolla; and a superior ovary. [Illustration: THE MOSSY SAXIFRAGE.] Several of the Saxifrages grow in rocky and stony places, and four or five species are sufficiently common to demand a notice here. The flowers of this group have a calyx of five sepals that is either quite free or more or less adherent to the ovary; a corolla of five petals; ten stamens, attached with the petals at the base of the calyx; and a two-celled ovary, with two distinct styles, containing several seeds. Our first species is the London Pride, None-so-Pretty, or St. Patrick's Cabbage (_Saxifraga umbrosa_), a native of Irish mountains which has been introduced into Britain as a garden flower, and has now become established as a wild flower in many parts. Its flowering stem grows from six to twelve inches high; and the small white or pink flowers bloom during June and July. [Illustration: THE IVY-LEAVED TOADFLAX.]