The genus Euphorbia is well known by the British weed called Caper Spurge, and the showy stove plants which belong to it. The male and female flowers are distinct; but both are inclosed in one cup-like involucre. In _fig._ 144, _a_ is the involucre, _b_ the female flower, and _c_ the male ones. The fruit (_fig._ 145) consists of three carpels, each containing a single seed, which divide with elasticity when the seeds are ripe. All the plants belonging to this order have a milky, glutinous juice when young, which in some genera becomes solid when exposed to the air. This is particularly the case with Siphonia Hevea, a Brazilian tree, the sap of which yields the Indian rubber used for Macintosh cloaks, &c.; it being more suitable for that purpose than the caoutchouc yielded by the _Ficus elastica_, which is the true Indian Rubber. The principal other genera belonging to this order are the Box (_Buxus_), the tree kind of which yields the wood used for wood-engraving, and the dwarf variety is employed as edging for gardens; Croton, an annual species of which (_Croton Tiglium_) yields the celebrated Croton oil; the Cassava (_Jatropha Manihot_), which though poisonous in a raw state, becomes the wholesome food called tapioca, when properly prepared; Palma Christi (_Ricinis communis_), from the seeds of which castor-oil is made; and the Manchineel tree (_Hippomane_), which is said to be so poisonous as to occasion the death of those who sleep beneath its shade. ORDER CLXVIII.—STACKHOUSEÆ. Small Australian shrubs with insignificant flowers. ORDER CLXIX.—ANTIDESMEÆ. East-Indian trees with inconspicuous flowers. ORDER CLXX.—URTICEÆ.—(SEE CHAP. X. P. 157.) The plants belonging to this order are divided into two sections, viz. those with tough fibres, as the Hemp, the Nettle, &c.; and those with milky sap, such as the Fig, the Mulberry, the Bread-fruit, &c. All the genera have the male and female flowers separate. The male flowers have four stamens which spring back and discharge their pollen with elasticity, and the female flowers have a one-celled ovary with two long stigmas. ORDER CLXXI.—ULMACEÆ. The principal genera are the Elm (_Ulmus_), the Nettle-tree (_Celtis_), and the Zelkoua-tree (_Planera_). The flowers, though very small, are pretty, from their opening in clusters before the leaves; and each has four stamens, with dark purple anthers, and is furnished with dark brown bracts. The fruit is a utricle, having a single seed, encircled by a broad thin transparent membrane. The leaves are rough, and their sides are unequal at the base. The bark of Elm trees is rough and deeply furrowed; and the roots spread, instead of penetrating deeply into the ground like those of the Oak. ORDER CLXXII.—PIPERACEÆ.