MAMMILLARIA  .-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 . EcxnNOCACTUS (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 cylin- drical, 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 Mammillaria, 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 5o 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 FIG .

2.—Echinoc¢ctus much upwards of 50,000 on a single reduced; the flowers are several plant . These spines are used by inches in

diameter . 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 . CEREUs.—This group bears the common name of torch thistle . It comprises about too species, largely Mexican but scattered through South America and the West Indies . The sterns are colum nar or elongated, some of the latter creeping on the ground or climbing up the trunks of trees, rooting as they grow . C. giganteus, the largest and most striking species of the genus, is a native of hot, arid, desert regions of New Mexico, growing there in rocky valleys and on mountain sides, where the tall stems with their erect branches have the appearance of telegraph poles . The stems grow to a height of from 50 ft. to 6o ft., and have a diameter of from t ft. to 2 ft., often unbranched, but sometimes furnished with branches which grow out at right angles from the main stem, and then curve upwards and continue their growth parallel to it; these stems have from twelve to twenty ribs, on which at intervals of about an inch are the buds with their thick yellow cushions, from which issue five or six large and numerous smaller spines . The fruits of this plant, which are green oval bodies from 2 to 3 in. long, contain a crimson pulp from which the Pimos and Papagos Indians prepare an excellent preserve; and they also use the ripe fruit as an article of food, gathering it by means of a forked stick attached to a long pole . The Cereuses include some of our most interesting and beautiful hothouse plants . In the allied genus Echinocereus, with 25 to 30 species in North and South America, the stems are short, branched or simple, divided into few or many ridges all armed with sharp, formidable spines .

E. pectinatus produces a purplish fruit resembling a

gooseberry, which is very good eating; and the fleshy part of the stem itself, which is called cabeza del viego by the Mexicans, is eaten by them as a vegetable after removing the spines .