This genus, which comprises nearly 300 species, mostly Mexican, with a few Brazilian and West Indian, is called nipple cactus, and consists of globular or cylindrical succulent plants, whose surface instead of being cut up into ridges with alternate furrows, as in Melocactus, is broken up into teat-like cylindrical or angular tubercles, spirally arranged, and terminating in a radiating tuft of spines which spring from a little woolly cushion. The flowers issue from between the mammillae, towards the upper part of the stem, often disposed in a zone just below the apex, and are either purple, rose-pink, white or yellow, and of moderate size. The spines are variously coloured, white and yellow tints predominating, and from the symmetrical arrangement of the areolae or tufts of spines they are very pretty objects, and are hence frequently kept in drawing-room plant cases. They grow freely in a cool greenhouse.
Fig. 2. - Echinocactus much reduced; the flowers are several inches in diameter.
Echinocactus (fig. 2) is the name given to the genus bearing the popular name of hedgehog cactus. It comprises some 200 species, distributed from the south-west United States to Brazil and Chile. They have the fleshy stems characteristic of the order, these being either globose, oblong or cylindrical, and either ribbed as in Melocactus, or broken up into distinct tubercles, and most of them armed with stiff sharp pines, set in little woolly cushions occupying the place of the buds. The flowers, produced near the apex of the plant, are generally large and showy, yellow and rose being the prevailing colours. They are succeeded by succulent fruits, which are exserted, and frequently scaly or spiny, in which respects this genus differs both from Melocactus and Mamrmllaria, which have the fruits immersed and smooth. One of the most interesting species is the E. ingens, of which some very large plants have been from time to time imported. These large plants have from 40 to 50 ridges, on which the buds and clusters of spines are sunk at intervals, the aggregate number of the spines having been in some cases computed at upwards of 50,000 on a single plant. These spines are used by the Mexicans as toothpicks.
The plants are slow growers and must have plenty of sun heat; they require sandy loam with a mixture of sand and bricks finely broken and must be kept dry in winter.