C. pleiogonus (twisted-angled); Fig. 26.—­An erect cylindrical-stemmed species, from 6 in. to 1 ft. high by 4 in. in diameter, with from ten to fourteen angles or ridges; these are somewhat tumid, and marked with depressions, from which the star-like clusters of spines spring, about a dozen spines in each cluster, the central one much the largest.  The flowers are about 8 in. long, the tube being rather thick and cylinder-like, expanding at the top, so as to form a sort of cup, in which the petals are arranged in several rows, with the middle filled by the numerous stamens, surmounted by the club-like pistil.  The colour of the flowers is purple-red.  This species appears to have first found its way into cultivation through some Continental garden, its native country being unknown.  It thrives only in a warm house, developing its flowers in summer.

[Illustration:  Fig. 26.—­Cereus pleiogonus.]

C. polyacanthus (many-spined).—­A newly-introduced species, from El Paso, in Mexico, where it is common on the sand ridges and stony hills.  Stem 10 in. high, 2 in. to 4 in. wide, pale green or glaucous, with about eight ridges, the spines being placed along the angles in clusters of half a dozen or so, and about 1/2 in. apart.  The flowers are 2 in. to 3 in. long; the tube spiny; the petals semi-erect and concave, rounded at the tip, and forming a shallow cup or wine-glass-like flower; the colour of the petals is deep blood-red.  This beautiful Cactus is exceptional in the length of time its flowers remain expanded and fresh, lasting a week or more; and as the plant is very free flowering, there is usually a beautiful display of rich red blossoms for about six weeks.  It may be grown in a cool greenhouse or window, requiring no artificial heat beyond what would be necessary to insure its protection from frost.  It flowers in spring.

C. procumbens (trailing); Fig. 27.—­This is a very pretty little Cactus, with spreading prostrate stems, from which upright branches grow to a height of 3 in. or 4 in.; they are 1/2 in. thick, generally only four-angled or square, with small spines in tufts along the angles.  The flowers are developed on the ends of the branches, and are 3 in. long and wide, the sepals spreading and recurved, as in a Paris daisy, their colour being bright rose purple.  The anthers form a corona-like ring, inclosing the upright, rayed stigma.  A native of Mexico; flowers in May and June.  In its native haunts we learn that this little Cactus is very free-flowering, but under cultivation in this country it flowers only rarely.  It thrives best when grown in a dry, sunny greenhouse, and kept perfectly dry during autumn and winter.  If allowed to get wet in that season, it is apt to rot, the stems being soft and watery.

[Illustration:  Fig. 27.—­Cereus procumbens.]