About two hundred species of echinocactus (See Figs. D, G, H), or hedgehog cactus, have been found in Mexico and various parts of South America. The globular, cylindrical, or oblong stems of these plants range in height from a few inches to nine feet. They are ridged. The ridges, which are furnished with large and small spines, take a vertical or spiral course, being sometimes divided, so as to form more or less distinct tubercules. The large showy flowers, with red, yellow, purple and white as prevailing colors, open several days in succession during bright weather.

The genera malacocarpus, gymnocalycium and astro-phytum, still referred to in trade lists, are now placed under echinocactus. E. myriostigma is one of the most singular plants. The stem attains a height of six or eight inches and is regularly divided into either five or six triangular ridges, upon the apex of which, at the summit of the plant, the pretty yellow flowers are freely borne. Spines are conspicuous by their absence, cushion-like tufts of short brownish hairs, regularly disposed along the apex of the ridges, appearing in their stead. The numerous small white spots which mark the surface have a very pleasing effect against the dark green epidermis. It is a native of Mexico, and commonly called the bishop's hood cactus; but the solidity of the plant, and its mathematical accuracy of form are more suggestive of the exact proportions of a well-executed metal casting than the work of a hatter.

The discocactus is a small genus of two or three species, which bear some resemblance to small echino-cacti. They are found in Brazil and the West Indies. The stems, bearing blunt spiny ridges, are about two inches high, and have the form of a flattened globe. The flowers emerge from a woolly mass at the top, and those of D. insignis have a very pleasant odor. Disco-cactus should not be confounded with the old genus disocactus, which is now referred to phyllocactus.

The species of cereus, over 200 in number (see Figs. A. Q, S), have a very extensive distribution, being found in temperate and tropical America, the West Indies, and Galapagos Islands. They are of erect or scandent habit, their stems, which vary in height from a few inches to 60 feet, being columnar, globose or triangular. Tufts of spines generally appear on the ridges of the cylindrical types, and also on the edges of the angular ones. The flowers are showy, sometimes fragrant, and some kinds produce the largest found in the family. These, however. are short-lived, and last only through the night during which they expand. The plants commonly known under the generic names of echinocereus, pilocereus and echinopsis, are now named only as sub-genera of cereus.

The thirteen species included under the genus phyllo-cactus are natives of tropical America, and grow among other epiphytes on the trunks of trees in dense forests. The stems are branching, jointed, flattened (leaf-like), or angular, and notched along the edges. The brilliant and conspicuous flowers proceed from the notches, and last a comparatively long time in perfection. In some species they are fragrant. The Disocactus biformis of Lindley is now placed in this genus.

There are only two species of epiphyllum, or lobster cactus - a name suggested by the color and elongated form of the flowers - but they are very beautiful plants, and inhabit the mountainous districts of Brazil, being found there on trees as epiphytes, and occasionally as terrestrial plants in dry, rocky situations. The jointed stems are flattened, and assume a somewhat cylindrical form when old. They are long and slender, droop gracefully and branch freely. The branches are composed of little pieces about two inches in length, truncate at the top and held together in the center. The margins are notched. The showy crimson or rose-colored flowers are borne in great profusion at the extremities. The genus rhipsalis, or mistletoe cactus (Figs. L and M) - the fruit resembles the berries of the mistletoe - includes about thirty species, which were formerly known under some one of the generic names, eu-rhipsalis, lepismium, hariota and pfeiffera. They are mostly natives of tropical America, only one species being found in the Old World. They are branching epiphytes, with flattened, angular or cylindrical stems and insignificant flowers.

The great variety of stem is their chief feature of interest.

Under nopalea (Fig. B) we have three species of plants which are distinguishable from opuntias only by technical characteristics of the reddish flowers.

The opuntias, or prickly pears (Figs. I,P,R,T) - in reference to the pear-like outline of the fruit - constitute a genus of over one hundred and fifty species They are, in common with nopaleas, natives of the warmer parts of America and the West Indies, being, perhaps, found in the greatest profusion in Mexico. The erect or decumbent fleshy stems branch freely, are jointed, flattened or cylindrical, sometimes tuberculed, and usually bear clusters of minute or coarse, barbed spines. Occasionally small fleshy leaves appear at the base of the spine clusters on the young stems, but they soon fall away. The majority of species may be readily known by the elliptical or oval form of the joints. The flowers are orange or yellow. Indian fig is another common name for members of this genus.

Some of the thirteen species of pereskia (Fig. J), natives of tropical America and the West Indies, would appear, from their shrub-like branches, leaves and flowers, to be connecting links between the more exceptional forms of cacti and ordinary vegetation. The stems, however, are succulent when young; but they become hard and woody with age, and bear the clusters of spines peculiar to cactaceous plants. The solitary or paniculate flowers are borne at the extremities of the young branches, and in some species resemble a single rose. They are very showy, the color being white, red or purple. P. aculcata is commonly known as the Barba-does gooseberry, from the resemblance of the fruit to that of the real gooseberry.

Comparatively few of these plants contribute toward the immediate necessities of man, but doubtless they are all of importance in the larger economy of nature. The untold generations through which they have existed, may ultimately result in the barren regions they inhabit becoming better adapted to the requirements of other plants, more useful in the arts and sciences. Dr. Carpenter, in bis "Physiological Botany," gives the following curious instance of their work, as civilizers of the earth : "On Mount Etna, for example, and its volcanic fields, it is the Indian fig which the Sicilians era-ploy to render such desolate regions susceptible of cultivation, This plant readily strikes into the fissures of the lava, and soon, by extending the ramifications of its roots into every crevice of the stone, and bursting the largest blocks asunder by their gradual increas, make it capable of being worked." The Mexicans eat the fleshy stems of Cereus peclinatus, which they call cabeza del Viego, as a vegetable; and they use the larger spines of Echinocactus Visnaga as toothpicks. The Mexican Indians use the fruit of the saguaro (Cereus giganteus) as an article of food. Several species of opuntia, particularly O. Tuna (Fig. T), yield the red, green or yellow fruits known as prickly pears.

These are sweet and juicy, and extensively used as dessert by the Mexicans and inhabitants of southern Europe. Their juice is used as a water color at Naples, and for coloring confectionary in the West Indies. The yellow fruits of the Barbadoes gooseberry are made into preserves by the people of the West Indies, and otherwise used as the English and Americans use ordinary gooseberries. Nopalea coccinellifera is valuable, in common with some species of the latter genus, as affording means of subsistence to the cochineal insects. In protracted seasons of drought, wild and domestic animals tear open the spiny covering of the fleshy-stemmed kinds of cactuses, such as melocactus, echinocactus, etc. and quench their thirst with the juicy interior, and travelers have frequently told of the numerous cases in which human lives have been saved through the timely refreshment afforded by those natural reservoirs on the desert plains of tropical countries.

Gerald Hastings.