HOUSELEEK, Sempervivum, a genus of ornamental ever green plants belonging to the family Crassulaceae. About 5o spe cies are known, some of which are hardy perennial herbs, and grow well in dry or rocky situations ; the others are evergreen shrubs or undershrubs, fit only for cultivation in the greenhouse or con servatory. The genus Sempervivum is distinguished from the nearly allied Sedum by having more than five (about I 2) petals, and by the glands at the base of the ovary being laciniated if present. The common houseleek, S. tectorum, is often met with in Great Britain on roofs (where it is sometimes planted to keep slates in position), and wall-tops, but is not a native. Originally it was indigenous in the Alps, but it is now widely dispersed in Eur ope, and has been introduced into America. The leaves are thick, fleshy and succulent, and are arranged in the form of a rosette, lying close to the soil. The plant propagates itself by offsets on all sides, so that it forms after a time a dense cushion or aggregation of rosettes. The flowering stem, which is of rather rare occurrence, is about I f t. high, reddish, cylindrical and succulent, and ends in a level-topped cyme, reflexed at the circumference, of reddish flowers, which bloom from June to September. Sedum acre (stone crop) is styled the little houseleek. S. glutinosum and S. balsasni f erum, natives respectively of Madeira and the Canary islands, contain a very viscous substance in large quantity, and are used for the preparation of bird-lime. S. arboreum is employed in Cyprus, the East, and northern Africa as an external remedy for malignant ulcers, inflammations and burns.