O. cochinellifera (cochineal-bearing); Bot.  Mag. 2742.—­An erect-growing plant, attaining a height of 9 ft. or more, and branching freely, the older parts of the stem and branches being woody and cylindrical; young joints flat, oblong-ovate, varying in length from 4 in. to 1 ft., deep green, rather soft and watery, spineless, the cushions distant, and sometimes bearing a few very short bristles.  Flowers at the extremities of the branches, 11/2 in. long, composed of numerous imbricating, scale-like petals, curving inwards, and coloured crimson.  Fruit flat-topped, 2 in. long, red; pulp reddish; seeds black.  It is a native of tropical South America, whence it was introduced in 1688.  It requires stove treatment, and blossoms in August.  This is one of the most useful of the genus, on account of its being the kind chiefly employed in the cultivation of cochineal.  It is one of the easiest to manage, requiring only a rather dry atmosphere, plenty of light, and a temperature not lower than 50 degs. in winter.  Syn.  Nopalea cochinellifera.

O. corrugata (wrinkled).—­Stem not more than 2 ft. high; joints cylindrical, wrinkled all over, about 2 in. long, covered with cushions of white hair or bristle-like spines.  Flowers 11/2 in. across, reddish-yellow, produced in August.  A native of Chili, whence it was introduced in 1824.  It may be grown in an ordinary greenhouse, on a shelf near the glass, and exposed to full sunshine.

O. curassavica (Curassoa); Pin-pillow.—­Branches spreading; joints cylindrical or club-shaped, dark green, bearing numerous cushions of woolly bristles, and long, white, very sharp-pointed spines.  Flowers 3 in. across, greenish-yellow, borne on the young joints in June.  Introduced from Curassoa in 1690.  A free-growing plant under favourable conditions, and one requiring stove treatment.  It has been cultivated in gardens almost as long as any species of Cactus.  There are several varieties of it known, differing from the type in habit, length of spine, or shade of colour in the flower.

O. cylindrica (cylindrical).—­Stem and joints cylindrical, the latter covered with spindle-shaped tubercles, each one crowned with a tuft of fine, hair-like, whitish spines, one or two in each tuft being stiff, and sharp as needles.  The leaves are fleshy, cylindrical, 1 in. or more long, and they remain on the joints longer than is usual in Opuntias.  Flowers crowded on the ends of the branches, each 1 in. in diameter, scarlet; they are developed in June.  This plant is said to grow to a height of 6 ft. or more in its native habitat, but under cultivation it is rarely seen more than 3 ft. high; it was introduced in 1799.  It is handsome and distinct enough to be worth growing.  It requires stove or greenhouse treatment, but rarely flowers under cultivation.

O. c. cristata (crested).—­A dwarf, cockscomb-like variety, with the leaves and white hairs growing all along the wrinkled top of the comb.  It is a very singular example of a “monster” Cactus.  It requires stove treatment.