The principal genus in this order is that of Mesembryanthemum, the Fig-marigold. In the species of this genus, the leaves are always thick and fleshy, and sometimes in very singular shapes; and sometimes they are covered with a sort of blistery skin, which makes them look as though covered with ice, as in the Ice-plant (_M. crystallinum_). The leaves, when this is the case, are said to be papulose. Some of the species are annuals, others shrubby, and others perennials; and they are all natives of the Cape of Good Hope. The flowers, which are generally showy, have a green, fleshy, tubular calyx, with a four or five cleft limb, the tubular part of which encloses the ovary; and a corolla of numerous very narrow petals, which are arranged in two or more series. The stamens are very numerous; and the capsule has four or more cells, each of which contains numerous seeds. The valves of the capsule open when the seeds are ripe, if the weather should be dry; but remain firmly closed, so long as the weather continues wet. The genera Reaumuria and Nitraria, which were formerly included in this order, have been removed from it, and made into separate orders, the latter of which is introduced here; and the genus Grielum, which was formerly included in Rosaceæ was first removed to Ficoideæ, and afterwards made into a separate order, under the name of Neuradiaceæ, which precedes Nitrariaceæ. ORDER XCIII.—CACTACEÆ.—THE CACTUS TRIBE. There is perhaps no order in the vegetable kingdom which embraces plants so singular in their forms as those comprehended in this tribe. All the genera, with the exception of Pereskia, are destitute of leaves, but they have all succulent stems which answer the purposes of leaves. The flowers of all the genera are extremely showy; the calyx and corolla are coloured alike, and confounded together; the stamens are numerous, with versatile anthers and very long filaments; the style is generally long and slender, and the stigmas are numerous, and either spreading or collected into a head. The ovary is in the tube of the calyx, and it becomes an eatable fruit, very similar to that of the gooseberry. The genera are all natives of tropical America. The principal kinds are the following: viz. Mammillaria, the stems of which are subcylindrical, and covered with tubercles, which are disposed in a spiral manner; and each of which is crowned with a little tuft of radiating spines mixed with down. The flowers are without stalks, and they are disposed in a kind of zone round the plant. The Melon Thistle or Turk’s-cap (_Melocactus communis_) has a globose stem with deep furrows, the projecting ribs having tubercles bearing tufts of spines. The stem is crowned with a woolly head, from which the flowers are protruded, the flowers themselves resembling those of Mammillaria, but being larger. The Hedgehog Thistles (_Echinocactus_) have stems resembling those of the different species of Melocactus, but they