O. spinosissima (very spiny).—­Stem erect, woody.  Joints very flat and thin, deep green, ovate or rotund, from 6 in. to 1 ft. long.  Cushions 1 in. apart.  Bristles very short.  Spines in clusters of about five, the longest 2 in. in length, brownish-yellow.  Flowers reddish-orange, small, usually only 2 in. across, produced in June.  A native of South America; naturalised in many parts of the Old World.  The stem becomes cylindrical with age, and sometimes is devoid of branches for about 5 ft. from the ground.  The plant requires stove treatment.  Probably this kind is only a form of O. Tuna.

O. subulata (awl-shaped).—­Stem erect, cylindrical, even below, channelled and tubercled above, about 2 in. in diameter.  Joints long and branch-like, with tufts of short, white hair on the apices of the tubercles, and one or two white, needle-like spines from 1/2 in. to 1 in. long.  At the base of each tuft, from the apex to 1 ft. or more down the younger branches, there is a fleshy, green, awl-shaped leaf, from 2 in. to 5 in. long.  Ultimately the leaves and spines fall away, the tubercles are levelled down, and the mature stem is regular and cylindrical, with tufts of white setae scattered over it.  Flowers small, produced in spring; sepals 2 in. long, green, deciduous; petals small, dull purple, usually about eight in each flower.  Fruit pear-shaped, 4 in. long; seeds very large, nearly 1/2 in. long and wide.  This handsome South American species was the subject of an interesting communication to the Gardeners’ Chronicle, in 1884, from Dr. Engelmann.  It had previously been known as a Pereskia from the fact of its leaves being persistent and very large.  In its leaves, flowers, and seeds, O. subulata is one of the most interesting of the genus.  It is easily grown in a warm greenhouse, and deserves a place in all collections of Cactuses.

O. Tuna (native name); Fig. 86.—­An erect-stemmed, flat-jointed, robust-growing species.  Joints ovate, 4 in. to 9 in. long, with cushions 1 in. apart, composed of short, fulvous bristles, and several long, needle-shaped, unequal, yellowish spines.  Flowers borne on the upper edges of the last-ripened joints, 3 in. across, reddish-orange, produced in July.  Fruit rich carmine, about 3 in. long, pear-shaped.  The plant is a native of the West Indies, &c., and was introduced in 1731.  It has already been stated, under O. spinosissima, that there is a close similarity between that species and O. Tuna.  We suspect, also, that O. nigricans is another near relation of these two.  They are much alike in all characters, and they require the same treatment.  O. Tuna has been seen as much as 20 ft. in height.

[Illustration:  Fig. 86.  Opuntia tuna.]

O. tunicata (coated-spined).—­Stem sub-erect, cylindrical.  Joints club-shaped, variable in length, about 2 in. in diameter.  When young the surface is broken up into numerous oblong tubercles, each bearing a small cushion of whitish, short hairs, and about half a dozen white spines, unequal in length, the longest stout, and inclosed in a hard sheath, which becomes broken and ragged when old.  Flowers not known.  A native of Mexico, and introduced in 1840.  It requires stove treatment.