This plant is difficult to preserve in health, the best method being that of grafting it on to a short Cereus, or a robust kind of Mamillaria, such as M. cirrhifera.  It is a pretty plant at all times, even when dead, for we have seen plants of it preserve the appearance of live specimens long after they have rotted and dried up in the centre, nothing remaining but the shell formed by the skin and silvery spines.  There is a close resemblance between this species and M. Grahami.

M. stella-aurata (golden star).—­This little plant obtains its name from the rich golden-yellow of its stellate clusters of spines, which are arranged thickly on the tips of the small, pointed tubercles.  It belongs to the group called Thimble Cactuses, of which it is one of the prettiest.  The stems are tufted, branching freely at the base, and rising to a height of about 2 in.  Flowers small, whitish, and much less ornamental than the berry-like fruits which succeed them, and which are egg-shaped, 1/2 in. long, and a deep rose-colour.  M. tenuis is a variety of this, with almost white spines.  Native of Mexico.  Introduced 1835.  May be cultivated under a bell-glass in a room window, the only danger being damp during winter, which must be carefully avoided.

M. sub-polyhedra (usually many-sided); Fig. 71.—­Stem simple till it becomes old, when it develops offsets at the base, broadly cylindrical, 8 in. high, 5 in. in diameter.  Tubercles four-sided at base, prism-shaped, bearing pads of white wool in the corners at the base, and crowned with tufts of from four to seven spines, usually all radial, sometimes one central.  The flowers, which usually appear in May, are arranged in a zone on the top of the old stems; sepals greenish-yellow, petals bright red.  Fruit 1 in. long, pear-shaped, scarlet.  Native of South Mexico, at high elevations.  It may be grown outside in summer, and wintered in a heated greenhouse or frame.  This is a singular-looking plant, the tubercles having an appearance suggestive of carving.  It is a slow grower, and requires careful attention in winter, when sometimes the roots all perish and the base of the stem rots.

[Illustration:  Fig. 71.  Mamillaria sub-polyhedra.]

M. sulcolanata (woolly-grooved); Fig. 72.—­Stem simple when young, proliferous at the sides when old, the young plants developing from the apices of the tubercles, and not in the axils, as is usual.  The tubercles are nut-shaped, large, the bases surrounded by white wool, the points bearing eight to ten rigid, brown spines, all radiating from a little pad of wool.  Flowers large, nearly 2 in. across, bright yellow, poppy-scented, the spread of the petals suggesting Paris Daisies; they are freely developed on the apex of the stem in June, and on till August.  Fruit egg-shaped, glaucous-green.  Native country, South Mexico; introduced 1836.  This charming little plant should be grown in a frame exposed to full sunshine all summer, and removed to a shelf in a warm greenhouse in winter.  With such treatment it grows and flowers freely.  Grafted on to a Cereus or Opuntia it is healthier than when on its own roots.