The flowers of all the species of Oxalis, the Wood-sorrel, are very pretty. The flowers have five regular petals, each furnished with a claw; and the petals are spirally twisted in the bud. There are ten stamens, and five styles. The capsule is five-celled, and five or ten valved, the valves opening lengthways. Most of the species are natives of South America, and greenhouse plants in England. ORDER LIV.—ZYGOPHYLLEÆ.—THE BEAN-CAPER TRIBE. The flowers of the Bean-caper are usually yellow; and the five petals are long, narrow, and placed widely apart. The botanic name of Zygophyllum signifies “with the leaves in pairs,” and this is the case to a remarkable degree. _Fagonia cretica_ is a very pretty plant, with purple flowers very much like those of Clarkia; and _Guiacum_, the Lignum Vitæ, is remarkable for the hardness of its wood and the gum it produces. Melianthus belongs to this order. ORDER LV.—RUTACEÆ.—THE RUE TRIBE. This order has been divided into four sections; three of which contain well-known plants, and have been divided into three orders by many botanists. The Rue (_Ruta graveolens_) is well known from its strong and disagreeable smell, which is produced by the oil secreted in transparent cells in the leaves, which have the appearance of dots, when the leaves are held up to the light. The leaves are of a bluish green, and the flowers of a greenish yellow; the latter growing in cymes at the end of the branches. There are four sepals, four petals, and eight stamens. There are four carpels, seated on an elevated receptacle, and each containing one cell, which grow into a four-celled fruit. In Fraxinella (_Dictamnus_) the petals are unequal; there are ten stamens, one style, and the carpels are two-seeded. In Diosma there are only five stamens, the style is arched, and the capsule consists of five-horned carpels. In Corræa the leaves are opposite; there are eight stamens, and the four petals grow together into a tube at the base; and in Crowea there are five sepals, five petals, and ten stamens; the leaves are also alternate. The Diosmas have as strong a scent as the Rue, and a perfume is made from them called Bucku at the Cape of Good Hope, of which country they are natives. The section Zanthoxyleæ contains the Zanthoxylum, also called the Toothache Tree, or Prickly Ash, a native of North America, the bark of which is very fragrant, and is said to be a cure for toothache and rheumatism; Ptelea or Shrubby Trefoil; and _Ailantus glandulosa_. _Zanthoxylum fraxineum_ has very pretty pinnate leaves, and small purple flowers; _Ptelea trifoliata_ has curiously winged fruit, which resemble those of the elm; and the Ailantus has remarkably long compound leaves, one leaf having been known to have fourteen pairs of leaflets, and to be upwards of three feet long. The two following orders are included in Rutaceæ by some botanists. ORDER LVI.—SIMARUBACEÆ.