Cactus, a genus of plants, the type of the natural order cactacem, comprising numerous species, all of which are natives of America. The name was originally given by Theophras-tus to a spiny plant of Sicily. The cactuses have fleshy and succulent, globular or columnar, often deeply channelled and many-jointed stems, usually leafless, but armed with spines and bristles. The structure of many of the species is singular and grotesque, and their appearance is interesting by reason of the roughness of the stalks and the beauty of the flowers. Found chiefly in the hot stony places of tropical America, their stems are filled with an abundant juice, which, being enclosed within a tough and impermeable skin, enables them to support a sluggish vital action without inconvenience in a parched soil. They vary in stature from creeping stems to angular ascending trunks, sometimes 30 feet in height. The flowers, varying from pure white to rich scarlet and purple, are much increased in size and brilliancy by cultivation in gardens and greenhouses. They thrive, however, only in the poorest soil. More than 60 species of cactuses have been described.
The G. melocactus, the great melon thistle, or Turk's cap, grows from the apertures of rocks in the dryest and hottest parts of America; it appears like a green melon, with deep ribs, set all over with sharp thorns, and was likened by Linnaeus to a hedgehog; it has on the top a small discoid, villous cap, from which the flowers grow in a circle; it attains the height of four or five feet in the West Indies, and has been brought to more than half this size in England; in times of drought they are ripped up by the cattle and their moist internal part greedily devoured. The G. grandifiorus is remarkable for its large, beautiful, sweet-scented flowers, which begin to open in the evening, and close again for ever before morning; the calyx, nearly one foot in diameter, is of a splendid yellow, enclosing pure white petals, and the flower during the five or six hours of its continuance is hardly surpassed in beauty; its structure is such that in cultivation it may be trained against a wall. The G. flagelliformis is a more delicate species than the preceding, with a greater number of smaller pink flowers, which keep open three or four days; its slender trailing branches require support.
The C. Opuntia, prickly pear, or Indian fig, derives its name from Opus, in Greece, where it was indigenous, although, like the others, a native of America; it also grows wild in Italy, and flourishes in the lava at the foot of Mount Etna; it is cultivated in England and America for its fruit. The G. tuna is used for hedging; three rows of it were planted as a boundary when the island of St. Christopher was divided between the English and the French. The G. cochinillifer is the chief nourishment of the cochineal insect; the delicate red juice of the fruit imparts a tinge to the urine. All the species of cactus are best cultivated in a sandy loam mixed with brick rubbish.