O. vulgaris (common); Bot.  Mag. 2393.—­A low, prostrate, spreading plant.  Joints short, oval, flattened, thicker than in O. missouriensis, 3 in. long by about 2 in. broad.  Spine-cushions 3/4 in. apart; tufts very small, with, occasionally, a long spine.  Leaves fleshy, very small.  Flowers 2 in. across, pale sulphur-yellow.  Fruits nearly smooth, 11/2 in. long, brown when ripe, with a strong disagreeable odour.  The flowers are produced freely in June.  The plant grows wild in Mexico, and extends up to New York, usually near the coast.  It is now common in many parts of Europe, where it has become naturalised.  In Madeira it has taken possession of all waste land, and is perfectly at home there.  In England it was cultivated by Gerard nearly 300 years ago.  It grows rapidly if planted in stony soil, in a position exposed to full sunshine, where it will creep along the ground, and root all along its stems, which rarely get elevated more than 6 in. from the ground.  This species and O. Ficus-indica are confused by some authors, owing, no doubt, to the name O. vulgaris having been given by a botanist to the latter, which is a much larger and very different-looking plant.  O. vulgaris is capable of withstanding our winters out of doors.

O. Whipplei (Captain Whipple’s).—­Stem usually prostrate, with slender, elongated branches, which are cylindrical when old, broken up into short joints when young.  Joints varying in length from 2 in. to 1 ft., less than 1 in. in diameter.  Cushions small, round.  Spines white, variable in number, and arranged in tufts on the ends of the tubercles, one being 1 in. long, the others shorter.  Flowers nearly 2 in. in diameter, red, borne in a cluster on the ends of the last-ripened joints in June.  Fruit 1 in. long, with a cavity in the top.  A compact, Mexican species, with crowded branches, and very free-flowering.  It requires stove treatment.  O. Whipplei is related to O. arborescens, from which, however, it is easily distinguished by the latter having a stout central spine and numerous radiating ones.

Of the 150 species of Opuntia known, about one-third have been selected for description here, and amongst these will be found all the best-marked kinds in the genus, and most of those of which we have any knowledge.  Botanists find good specific characters in the size and structure of the seeds, in the character of the fruits, &c.; but for horticultural purposes these are of little or no value.

CHAPTER XV.

THE GENUS PERESKIA.

(Named in honour of Nicholas F. Peresk, a botanist of Provence.)