[Illustration:  Fig. 73.  Mamillaria vivipara radiosa.]

M. Wildiana (Wild’s).—­An old garden Cactus, and one of the prettiest of the tufted, small-stemmed kinds.  Its largest stems are 3 in. high by about 11/2 in. in diameter, and bear spiral rows of clavate, dark green, crystallised tubercles, 1/2 in. long, with about ten radial white spines, 1/2 in. long, the three upper spines, together with the solitary central hooked one, being yellow.  Flowers small, numerous on the apices of the stems, rose-coloured, lined with purple; they are developed in summer.  This also forms dense tufts of stems.  A specimen at Kew, only a few years old, has already over thirty heads.  It is a native of Mexico, at an altitude of 5000 ft., growing on lava and basalt, and even on the trunks of trees.  For its cultivation, a shelf in a sunny greenhouse is a most suitable position, both in winter and summer.  Introduced 1835.

M. Wrightii (Wright’s).—­This is a charming little plant, of something the same character as M. dolichocentra.  It has not long been cultivated in gardens, but being easy to manage, and exceptionally pretty, it is sure to become a favourite as it gets known.  Stem rounded above, narrowed and peg-top-like at the base, the top flattened, about 3 in. across, height about the same.  Tubercles conical, 1/2 in. long, shining green, and bearing a tuft of six or eight spines, which are straight, hair-like, white, and 1/2 in. long; there are two central spines, of same length, and hooked.  Flowers in the top of the stem, 1 in. long and wide, bright purple; they are succeeded by egg-shaped, purple berries, 1 in. long, and prettily arranged among the tubercles.  In England a warm house seems most suitable for this species.  It likes plenty of moisture and sunlight during the summer, whilst making new growth; but in winter, when at rest, it ought to be kept on a shelf, and just moistened overhead in bright weather.  There are healthy examples of it at Kew.  Flowering season, May and June.  Native country, Mexico.  Introduced about 1878.

M. Zucchariniana (Zuccharini’s).—­Stem simple, globose, often attaining a height of 10 in. by about 7 in. in diameter.  Tubercles dark green, conical, 1/3 in. long, 1/2 in. broad at base, naked at the point, but with four to six spines springing from the areole a little below the point; spines ash-coloured, stiff, black-tipped.  Flowers in a ring about the top of the stem, length 1 in., the tube enveloped in long, black, twisted hairs; sepals brown-purple; petals narrow, sharp-pointed, purple-rose coloured; stamens white and yellow; stigma rose-coloured.  Flowers in June and July.  Native of Mexico.  A large, handsome-stemmed kind, easily kept in health, and flowering freely if grown on a shelf in a cool greenhouse in winter, and placed in a warm, sunny position out of doors in summer.  It produces seeds freely, and pretty plants, 3 in. or more in diameter, may be obtained in two years from seeds.  By grafting it, when young, on the stem of a Cereus or cylindrical Opuntia, a healthy, drumstick-like plant is easily obtained.