Species.

P. aselliformis (woodlouse-like); Fig. 75.—­The size, habit, and structure of this plant are so well represented in the Figure that little description is necessary.  The stems are simple till they get about 3 in. high, when they develop offsets about the base, which may either be removed to form new plants, or allowed to remain and grow into a specimen like that in the Illustration.  The flowers are large for the size of the plant, and they are developed freely in the apex of the stems in the early part of the summer.  The tube is very short, naked, and completely hidden by the young mammae; sepals and petals in four series, the outer one pale purple, the inner of a deep purple colour; stamens very numerous, and the stigma has only four erect lobes.  The plant was first described from examples cultivated in Berlin in 1843, but the flowers were not known till 1858.  There are several varieties known, viz., P. a. concolor, which is distinguished by the whole of the flower being deep purple in colour; P. a. pectinata has larger scales (spine-tufts); and P. a. cristata is, as its name denotes a kind of cockscomb or crested form.  They are all natives of Mexico.

CHAPTER XIV.

THE GENUS OPUNTIA.

(The old Latin name used by Pliny, and said to have been derived from the city of Opus.)

There are about 150 species of Opuntia known, all of them natives of the American continent and the West Indies, though a considerable number have become naturalised in many other parts of the world.  They are, with very few exceptions, easily distinguished from all other Cactuses by the peculiar character of their stems and spines; they are also well marked in the structure of their flowers.  They vary in size from small, trailing, many-branched plants, never exceeding 6 in. in height, to large shrubs 8 ft. to 30 ft. high. (Humboldt states that he saw “Opuntias and other Cactuses 30 ft. to 40 ft. high.”) Generally the branches are nearly flat when young, and shaped like a racquet or battledore; but in some species the branches are round (i.e., in O. cylindrica, O. subulata, O. arborescens, &c.).  All the kinds have fleshy stems, which ultimately become cylindrical and woody.  At first they consist of fleshy joints, superposed upon one another, the joints varying considerably in size and shape.  When young they bear small fleshy leaves along with the spine-tufts; but the former fall off at an early stage, whilst the spines are altered in length or number as the joints get old.  In one or two kinds the spines fall away when the joints begin to harden, and in O. subulata the leaves are large and persistent.