Rue is a well-known shrub with small pinnate leaves, and possessing a strong and very disagreeable odour; this depends upon the volatile oil which is contained in the glands with which the leaves are dotted. It has been, from time immemorial, used as a medicine. Another member of this order, the Buchu (Diosmia crenata), is also used medicinally. [Illustration: Rue.] 19. OXALIDACEÆ (Oxalis acetosella) Wood Sorrel. The Wood Sorrel is very acid, and from its juice is made the salt of sorrel (which is bin-oxalate of potash), used to get out ink and iron stains from linen, &c. This is supposed to be the true Shamrock. [Illustration: Wood Sorrel.] This completes the orders of Thalamifloræ, which, with the following sub-class, Calycifloræ, contain all our star-like flowers, or those in which the corolla forms a whorl or open ring of petals. The third sub-class contains those chiefly in which the flowers form cups or bells. ORDERS OF CALYCIFLORÆ. 1. CELASTRACEÆ (Euonymus Europæas) Spindle Tree. [Illustration: Spindle Tree.] This order consists of shrubs or small trees growing in the temperate regions of most parts of the world, and some of the species, as Celastrus venatus, are said to be poisonous; the seeds of the South African species are used to express oil from. 2. RHAMNACEÆ (Rhamnus catharticus) Buckthorn. (Rhamnus frangula) Black Alder. [Illustration: Buckthorn.] Buckthorn berries afford a juice which, when made into syrup with sugar, is a popular purgative medicine; the juice precipitated with lime produces the green pigment known to artists as "sap green." The "French Berries" used as a yellow dye-stuff are procured from a species of Rhamnus. 3. FABACEÆ, or } (Cytisus scoparius) Broom. LEGUMINOSÆ } (Pisum sativum) Garden Pea. (Faba vulgaris) Garden Bean. [Illustration: Broom.] [Illustration: Garden Pea.] The plants producing pods or legumes are among the most important of the orders of this class, giving us very many useful and nutritious plants, which, for the most part, are climbers, as Peas, Beans, &c. The Tamarind and Cassia trees belong to this order, also those which produce gum-arabic, catechu, logwood, and indigo. There are between six and seven thousand species of the Leguminosæ. 4. ROSACEÆ (Rosa centifolia) Hundred-leaved Rose. (Fragaria vesca) Wood Strawberry. (Rubus fruticosus) Bramble. (Pyrus communis) Pear Tree.