The grotesque forms of the Cactuses possess the stiff rigidity of the aloes. Their fleshy stems, covered with a gray-green coriaceous rind, generally exhibit bunches of hair and thorns instead of leaves. The angular columns of the Cerei, or torch-cactuses, rise to the height of sixty feet,--generally branchless, sometimes strangely ramified, as candelabras, while others creep like ropes upon the ground, or hang, snake-like, from the trees, on which they are parasitically rooted. The opuntias are unsymmetrically constructed of thick flat joints springing one from the other, while the melon-shaped Echinocacti and Mammillariæ, longitudinally ribbed or covered with warts, remain attached to the soil. The dimensions of these monstrous plants are exceedingly variable. One of the Mexican echinocacti (_E. Visnaga_) measures four feet in height, three in diameter, and weighs about two hundred pounds; while the dwarf cactus (_E. nana_) is so small that, loosely rooted in the sand, it frequently remains sticking between the toes of the dogs that pass over it. The splendidly coloured flowers of the cactuses form a strange contrast to the deformity of their stems, and the spectator stands astonished at the glowing life that springs forth from so unpromising a stock. These strange compounds of ugliness and beauty are in many respects useful to man. The pulp of the melocacti, which remains juicy during the driest season of the year, is one of the vegetable sources of the wilderness, and refreshes the traveller after he has carefully removed the thorns. Almost all of them bear an agreeable acid fruit, which, under the name of the Indian fig, is consumed in large quantities in the West Indies and Mexico. The light and incorruptible wood is admirably adapted for the construction of oars and many other implements. The farmer fences his garden with the prickly opuntias; but the services which they render, as the plants on which the valuable cochineal insect feeds and multiplies, are far more important. The cactuses prefer the most arid situation, naked plains, or slopes, where they are fully exposed to the burning rays of the sun, and impart a peculiar physiognomy to a great part of tropical America. None of the plants belonging to this family existed in the Old World previously to the discovery of America; but some species have since then rapidly spread over the warmer regions of our hemisphere. The Nopal (_Cactus Opuntia_) skirts the Mediterranean along with the American agave, and from the coasts has even penetrated far into the interior of Africa, everywhere maintaining its ground, and conspicuously figuring along with the primitive vegetation of the land.