E. cylindraceus (cylindrical).—­A large-growing kind, attaining a height of several feet, very broad, and, as the name denotes, cylindrical in shape.  When large, the stem often develops lateral branches about its base.  Cultivated plants of it are 6 in. high, the sides marked with about a score of ridges, upon which, arranged in a dense cluster, are the stout, strong spines, the longest of them 3 in. long, hooked, and projecting outwards, the shorter spreading and interlacing so as to form a sort of spiny network all round the stem.  The flowers are yellow, 2 in. long, and are composed of a short, thick tube bearing from forty to fifty fringed sepals, and about half that number of petals, which are also fringed.  There are as many as a dozen flowers opened together on stout, aged plants; it is, however, more because of the densely spinous stems than the flowers that this species has found its way into cultivation.  It cannot be recommended for any except large collections, and where it can be grown in a stove temperature.  It is a native of the hot deserts of Colorado, and was introduced about ten years ago.  There are several healthy young specimens of it in the Kew collection.

E. echidne (viper; probably in allusion to the fang-like spines).—­This species is remarkable in having a stout cylindrical stem, 12 in. high by 8 in. wide, with about a dozen deep ridges; these are disposed spirally, and bear tufts of rigid, broad spines, 1 in. or more long, spreading, so as to interlace and form a wire-like network all round the stem.  It may be mentioned here that an American naturalist has recently suggested that the object of these iron-like spines on the stems of many Cactuses, and more especially on the majority of the Hedgehog kinds, is not so much to defend the fleshy stems from browsing animals as to afford protection from the scorching rays of the sun, which would otherwise cause the stems to blister and shrivel; and the nature of the spiny covering of E. echidne seems to support such a view.  As in many others, the clusters of spines in this plant have their bases embedded in a tuft of whitish wool.  The flowers are developed near the centre of the top of the stem, and are of medium size, bright yellow, with whitish stamens; they are produced two or three together, in summer.  This species is a native of Mexico; it thrives in a greenhouse where frost is excluded, but only rarely flowers with us under cultivation.

E. Emoryi (Emory’s); Fig. 34.—­This is a very large-stemmed kind, specimens having been found nearly 3 ft. in height and about 2 ft. in diameter.  Smaller plants, such as are in English collections, have globose stems 1 ft. through, with about thirteen ribs, the ribs tuberculated, the tubercles large, and rounded; the spines are borne on the apex of the tubercles in star-shaped bundles of eight or nine, and are angled, often flat on the top side, articulated, with hooked points, whilst in length they vary from