C. variabilis (variable); Bot.  Mag. 4084, under the name of C. pitajaya.  —­A tall-growing plant, rather straggling in habit, branching freely, the stems usually four-winged, but sometimes with three, five, or more, constricted at intervals, as in Phyllocactus, the wings spiny along the edges; spines 1 in. long.  Flowers on the sides of the stems, rather low down, long-tubed; large, showy; tube 6 in. long, smooth, fleshy, with a few scales near the top, and a whorl of greenish, strap-shaped, pointed sepals, the petals spreading, with toothed margins and a long acute point, white or cream-coloured; anthers yellow.  A native of various parts of South America and the West Indies, but always close to the sea.  It flowers in July; the flowers, which open generally in the evening, remain expanded all night, and close before noon the day following.  This species requires tropical or warm house treatment.  There are some old plants of it in the Kew collection, where it flowers annually.  Except for large houses, this species is not recommended for general cultivation, as it blossoms only after attaining a good size, and the stems, when old, are not at all ornamental.

CHAPTER VII.

THE GENUS ECHINOCACTUS.

(From echinos, a hedgehog, and Cactus.)

Many of the plants included in the genus Echinocactus are very similar in habit and stem-characters to the Cereus.  Botanists find characters in the seed vessel (ovary) and in the seeds by which the two genera are supposed to be easily separable; but, so far as can be made out by a comparison of their more conspicuous characters, there is very little indeed to enable one to distinguish the two genera from each other when not in flower.  A comparison of the figures given in these pages will show that such is the case.

The name Echinocactus was given to E. tenuispinus, which was first introduced into English gardens in 1825.  The spiny character of this species is surpassed by that of many of the more recently introduced kinds; still it is sufficient to justify its being compared to a hedgehog.  Some of the kinds have spines 4 in. long, broad at the base, and hooked towards the point, the hooks being wonderfully strong, whilst in others the spines are long and needle-like, or short and fine as the prickles on a thistle.  The stems vary much in size and form, being globose, or compressed, or ovate, a few only being cylindrical, and attaining a height of from 5 ft. to 10 ft.  They are almost always simple—­that is, without branches, unless they are compelled to form such by cutting out or injuring the top of the stem; the ridges vary in number from about five to ten times that number, and they are in some species very firm and prominent, in others reduced to mere undulations, whilst in a few, they are separated into numerous little tubercles or mammae.  The species are nearly all possessed of spines, which are collected in bundles along the