1911 Encyclopædia Britannica/Cactus

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CACTUS. This word, applied in the form of Κάκτος by the ancient Greeks to some prickly plant, was adopted by Linnaeus as the name of a group of curious succulent or fleshy-stemmed plants, most of them prickly and leafless, some of which produce beautiful flowers, and are now so popular in our gardens that the name has become familiar. As applied by Linnaeus, the name Cactus is almost conterminous with what is now regarded as the natural order Cactaceae, which embraces several modern genera. It is one of the few Linnaean generic terms which have been entirely set aside by the names adopted for the modern divisions of the group.

FIG. 1.—Prickly Pear (Opuntia vulgaris). 1, Flower reduced; 2, Same in vertical section; 3, Flattened branch much reduced; 4, Horizontal plan of arrangement of flower.

The Cacti may be described in general terms as plants having a woody axis, overlaid with thick masses of cellular tissue forming the fleshy stems. These are extremely various in character and form, being globose, cylindrical, columnar or flattened into leafy expansions or thick joint-like divisions, the surface being either ribbed like a melon, or developed into nipple-like protuberances, or variously angular, but in the greater number of the species furnished copiously with tufts of horny spines, some of which are exceedingly keen and powerful. These tufts show the position of buds, of which, however, comparatively few are developed. The stems are in most cases leafless, using the term in a popular sense; the leaves, if present at all, being generally reduced to minute scales. In one genus, however, Peireskia, the stems are less succulent, and the leaves, though rather fleshy, are developed in the usual form. The flowers are frequently large and showy, and are generally attractive from their high colouring. In one group, represented by Cereus, they consist of a tube, more or less elongated, on the outer surface of which, towards the base, are developed small and at first inconspicuous scales, which gradually increase in size upwards, and at length become crowded, numerous and petaloid, forming a funnel-shaped blossom, the beauty of which is much enhanced by the multitude of conspicuous stamens which with the pistil occupy the centre. In another group, represented by Opuntia (fig. 1), the flowers are rotate, that is to say, the long tube is replaced by a very short one. At the base of the tube, in both groups, the ovary becomes developed into a fleshy (often edible) fruit, that produced by the Opuntia being known as the prickly pear or Indian fig.

The principal modern genera are grouped by the differences in the flower-tube just explained. Those with long-tubed flowers comprise the genera Melocactus, Mammillaria, Echinocactus, Cereus, Pilocereus, Echinopsis, Phyllocactus, Epiphyllum, &c.; while those with short-tubed flowers are Rhipsalis, Opuntia, Peireskia, and one or two of minor importance. Cactaceae belong almost entirely to the New World; but some of the Opuntias have been so long distributed over certain parts of Europe, especially on the shores of the Mediterranean and the volcanic soil of Italy, that they appear in some places to have taken possession of the soil, and to be distinguished with difficulty from the aboriginal vegetation. The habitats which they affect are the hot, dry regions of tropical America, the aridity of which they are enabled to withstand in consequence of the thickness of their skin and the paucity of evaporating pores or stomata with which they are furnished,—these conditions not permitting the moisture they contain to be carried off too rapidly; the thick fleshy stems and branches contain a store of water. The succulent fruits are not only edible but agreeable, and in fevers are freely administered as a cooling drink. The Spanish Americans plant the Opuntias around their houses, where they serve as impenetrable fences.

MELOCACTUS, the genus of melon-thistle or Turk's-cap cactuses, contains, according to a recent estimate, about 90 species, which inhabit chiefly the West Indies, Mexico and Brazil, a few extending into New Granada. The typical species, M. communis, forms a succulent mass of roundish or ovate form, from 1 ft. to 2 ft. high, the surface divided into numerous furrows like the ribs of a melon, with projecting angles, which are set with a regular series of stellated spines—each bundle consisting of about five larger spines, accompanied by smaller but sharp bristles—and the tip of the plant being surmounted by a cylindrical crown 3 to 5 in. high, composed of reddish-brown, needle-like bristles, closely packed with cottony wool. At the summit of this crown the small rosy-pink flowers are produced, half protruding from the mass of wool, and these are succeeded by small red berries. These strange plants usually grow in rocky places with little or no earth to support them; and it is said that in times of drought the cattle resort to them to allay their thirst, first ripping them up with their horns and tearing off the outer skin, and then devouring the moist succulent parts. The fruit, which has an agreeably acid flavour, is frequently eaten in the West Indies. The Melocacti are distinguished by the distinct cephalium or crown which bears the flowers.

MAMMILLARIA.—This genus, which comprises nearly 300 species, mostly Mexican, with a few Brazilian and West Indian, is called nipple cactus, and consists of globular or cylindrical succulent plants, whose surface instead of being cut up into ridges with alternate furrows, as in Melocactus, is broken up into teat-like cylindrical or angular tubercles, spirally arranged, and terminating in a radiating tuft of spines which spring from a little woolly cushion. The flowers issue from between the mammillae, towards the upper part of the stem, often disposed in a zone just below the apex, and are either purple, rose-pink, white or yellow, and of moderate size. The spines are variously coloured, white and yellow tints predominating, and from the symmetrical arrangement of the areolae or tufts of spines they are very pretty objects, and are hence frequently kept in drawing-room plant cases. They grow freely in a cool greenhouse.

FIG. 2.—Echinocactus much reduced; the flowers are several inches in diameter.

ECHINOCACTUS (fig. 2) is the name given to the genus bearing the popular name of hedgehog cactus. It comprises some 200 species, distributed from the south-west United States to Brazil and Chile. They have the fleshy stems characteristic of the order, these being either globose, oblong or cylindrical, and either ribbed as in Melocactus, or broken up into distinct tubercles, and most of them armed with stiff sharp pines, set in little woolly cushions occupying the place of the buds. The flowers, produced near the apex of the plant, are generally large and showy, yellow and rose being the prevailing colours. They are succeeded by succulent fruits, which are exserted, and frequently scaly or spiny, in which respects this genus differs both from Melocactus and Mamrmllaria, which have the fruits immersed and smooth. One of the most interesting species is the E. ingens, of which some very large plants have been from time to time imported. These large plants have from 40 to 50 ridges, on which the buds and clusters of spines are sunk at intervals, the aggregate number of the spines having been in some cases computed at upwards of 50,000 on a single plant. These spines are used by the Mexicans as toothpicks. The plants are slow growers and must have plenty of sun heat; they require sandy loam with a mixture of sand and bricks finely broken and must be kept dry in winter.

CEREUS.—This group bears the common name of torch thistle. It comprises about 100 species, largely Mexican but scattered through South America and the West Indies. The stems are columnar or elongated, some of the latter creeping on the ground or climbing up the trunks of trees, rooting as they grow. C. giganteus, the largest and most striking species of the genus, is a native of hot, arid, desert regions of New Mexico, growing there in rocky valleys and on mountain sides, where the tall stems with their erect branches have the appearance of telegraph poles. The stems grow to a height of from 50 ft. to 60 ft., and have a diameter of from 1 ft. to 2 ft., often unbranched, but sometimes furnished with branches which grow out at right angles from the main stem, and then curve upwards and continue their growth parallel to it; these stems have from twelve to twenty ribs, on which at intervals of about an inch are the buds with their thick yellow cushions, from which issue five or six large and numerous smaller spines. The fruits of this plant, which are green oval bodies from 2 to 3 in. long, contain a crimson pulp from which the Pimos and Papagos Indians prepare an excellent preserve; and they also use the ripe fruit as an article of food, gathering it by means of a forked stick attached to a long pole. The Cereuses include some of our most interesting and beautiful hothouse plants. In the allied genus Echinocereus, with 25 to 30 species in North and South America, the stems are short, branched or simple, divided into few or many ridges all armed with sharp, formidable spines. E. pectinatus produces a purplish fruit resembling a gooseberry, which is very good eating; and the fleshy part of the stem itself, which is called cabeza del viego by the Mexicans, is eaten by them as a vegetable after removing the spines.

PILOCEREUS, the old man cactus, forms a small genus with tallish erect, fleshy, angulate stems, on which, with the tufts of spines, are developed hair-like bodies, which, though rather coarse, bear some resemblance to the hoary locks of an old man. The plants are nearly allied to Cereus, differing chiefly in the floriferous portion developing these longer and more attenuated hair-like spines, which surround the base of the flowers and form a dense woolly head or cephalium. The most familiar species is P. senilis, a Mexican plant, which though seldom seen more than a foot or two in height in greenhouses, reaches from 20 ft. to 30 ft. in its native country.

ECHINOPSIS is another small group of species, separated by some authors from Cereus. They are dwarf, ribbed, globose or cylindrical plants; and the flowers, which are produced from the side instead of the apex of the stem, are large, and in some cases very beautiful, being remarkable for the length of the tube, which is more or less covered with bristly hairs. They are natives of Brazil, Bolivia and Chile.

FIG. 3.—Branch of Phyllocactus much reduced; the flowers are 6 in. or more in diameter.

PHYLLOCACTUS (fig. 3), the Leaf Cactus family, consists of about a dozen species, found in Central and tropical South America. They differ from all the forms already noticed in being shrubby and epiphytal in habit, and in having the branches compressed and dilated so as to resemble thick fleshy leaves, with a strong median axis and rounded woody base. The margins of these leaf-like branches are more or less crenately notched, the notches representing buds, as do the spine-clusters in the spiny genera; and from these crenatures the large showy flowers are produced. As garden plants the Phyllocacti are amongst the most ornamental of the whole family, being of easy culture, free blooming and remarkably showy, the colour of the flowers ranging from rich crimson, through rose-pink to creamy white. Cuttings strike readily in spring before growth has commenced; they should be potted in 3-in. or 4-in. pots, well drained, in loamy soil made very porous by the admixture of finely broken crocks and sand, and placed in a temperature of 60°; when these pots are filled with roots they are to be shifted into larger ones, but overpotting must be avoided. During the summer they need considerable heat, all the light possible and plenty of air; in winter a temperature of 45° or 50° will be sufficient, and they must be kept tolerably dry at the root. By the spring they may have larger pots if required and should be kept in a hot and fairly moistened atmosphere; and by the end of June, when they have made new growth, they may be turned out under a south wall in the full sun, water being given only as required. In autumn they are to be returned to a cool house and wintered in a dry stove. The turning of them outdoors to ripen their growth is the surest way to obtain flowers, but they do not take on a free blooming habit until they have attained some age. They are often called Epiphyllum, which name is, however, properly restricted to the group next to be mentioned.

EPIPHYLLUM.—This name is now restricted to two or three dwarf branching Brazilian epiphytal plants of extreme beauty, which agree with Phyllocactus in having the branches dilated into the form of fleshy leaves, but differ in haying them divided into short truncate leaf-like portions, which are articulated, that is to say, provided with a joint by which they separate spontaneously; the margins are crenate or dentate, and the flowers, which are large and showy, magenta or crimson, appear at the apex of the terminal joints. In E. truncatum the flowers have a very different aspect from that of other Cacti, from the mouth of the tube being oblique and the segments all reflexed at the tip. The short separate pieces of which these plants are made up grow out of each other, so that the branches may be said to resemble leaves joined together endwise.

RHIPSALIS, a genus of about 50 tropical species, mainly in Central and South America, but a few in tropical Africa and Madagascar. It is a very heterogeneous group, being fleshy-stemmed with a woody axis, the branches being angular, winged, flattened or cylindrical, and the flowers small, short-tubed, succeeded by small, round, pea-shaped berries. Rhipsalis Cassytha, when seen laden with its white berries, bears some resemblance to a branch of mistletoe. All the species are epiphytal in habit.

OPUNTIA, the prickly pear, or Indian fig cactus, is a large typical group, comprising some 150 species, found in North America, the West Indies, and warmer parts of South America, extending as far as Chile. In aspect they are very distinct from any of the other groups. They are fleshy shrubs, with rounded, woody stems, and numerous succulent branches, composed in most of the species of separate joints or parts, which are much compressed, often elliptic or suborbicular, dotted over in spiral lines with small, fleshy, caducous leaves, in the axils of which are placed the areoles or tufts of barbed or hooked spines of two forms. The flowers are mostly yellow or reddish-yellow, and are succeeded by pear-shaped or egg-shaped fruits, having a broad scar at the top, furnished on their soft, fleshy rind with tufts of small spines. The sweet, juicy fruits of O. vulgaris and O. Tuna are much eaten under the name of prickly pears, and are greatly esteemed for their cooling properties. Both these species are extensively cultivated for their fruit in Southern Europe, the Canaries and northern Africa; and the fruits are not unfrequently to be seen in Covent Garden Market and in the shops of the leading fruiterers of the metropolis. O. vulgaris is hardy in the south of England.

The cochineal insect is nurtured on a species of Opuntia (O. coccinellifera), separated by some authors under the name of Nopalea, and sometimes also on O. Tuna. Plantations of the nopal and the tuna, which are called nopaleries, are established for the purpose of rearing this insect, the Coccus Cacti, and these often contain as many as 50,000 plants. The females are placed on the plants about August, and in four months the first crop of cochineal is gathered, two more being produced in the course of the year. The native country of the insect is Mexico, and it is there more or less cultivated; but the greater part of our supply comes from Colombia and the Canary Islands.

PEIRESKIA ACULEATA, or Barbadoes gooseberry, the Cactus peireskia of Linnaeus, differs from the rest in having woody stems and leaf-bearing branches, the leaves being somewhat fleshy, but otherwise of the ordinary laminate character. The flowers are subpaniculate, white or yellowish. This species is frequently used as a stock on which to graft other Cacti. There are about a dozen species known of this genus, mainly Mexican.