Propagation.—­This is usually effected by means of seeds, which may be procured from Continental seedsmen as well as from our own.  The treatment required by the seeds is similar to what has been already advised for those of other Cactuses.  The tufted kinds are easily multiplied by separating the stems, or even by cutting off the tops and planting them in small pots of sandy soil.

Species.  The following kinds are selected from those known to be in cultivation; of course, it is out of the question here to enumerate all the species known.

M. angularis (angular-tubercled).—­A robust kind, with stems 4 in. to 8 in. high, and branching somewhat freely; tubercles prism-shaped, rather thick at the base, and slightly angular, 1/4 in. long, their tops tufted with short white spines; at the base of the tubercles are little tufts of white wool.  Flowers are only rarely produced by cultivated plants; they are small, tubular, rosy-purple, the stamens yellow.  Introduced from Mexico in 1835; flowers in summer.  When happily situated, it forms a specimen 1 ft. in diameter, owing to its freely produced arm-like branches, which spread out and curve upwards.  It requires a warm greenhouse temperature during winter, and exposure to bright sunshine at all times.

M. applanata (flattened).—­In this, the stem is broader than high, and has a squat appearance; tubercles 3/4 in. long, cone-shaped, with stellate tufts of straight, hair-like spines, white when young, yellowish when aged.  Flowers springing from the outside of the stem-top, white, tinged with red.  It is a native of Mexico, and blossoms in summer.  A specimen, 6 in. through at the base, may be seen at Kew, where it has been for many years, without altering perceptibly in size.  All the larger-stemmed Mamillarias are exceedingly slow growers after they have reached a certain size, although, in the seedling stage, they grow freely.  The treatment for this kind should resemble that advised for the last.

M. atrata (blackened).—­Stem oval in shape, broad at the base, 4 in. high, unbranched; tubercles swollen, 1/2 in. long, deep green, cone-shaped, becoming flattened through pressure of growth.  Spines set in a tuft of white hairs, falling off from the lowest mammae, as happens in many of the thick-stemmed kinds.  Flowers numerous, and developed all round the outside of the stem, stalkless, nestling closely between the tubercles, and when expanded looking like starry buttons of a rosy-pink colour.  Native of Chili, flowering in autumn.  This species is rare in England, but is worth attention because of the prettiness of its flowers, the attractive form of its stem, and its reputed hardiness.  It will thrive in a cold frame, and requires protection from excessive wet only, rather than from cold.  Grown in a warm house, it becomes sickly, and is short-lived.