[Illustration:  Fig. 72.  Mamillaria sulcolanata.]

M. tetracantha (four-spined); Bot.  Mag. 4060.—­Stem the size and shape of an ostrich’s egg, thickly studded with small, conical tubercles, woolly at the base, the apices bearing each four spreading spines, 3/4 in. long, rather stout, straight, brown when young, becoming almost white with age.  Flowers numerous, small, arranged as in M. sanguinea, to which and M. cirrhifera this species is closely related.  They are bright rose in colour, with orange-yellow anthers, and are developed in July.  Native of Mexico.  Requires the same treatment as M. cirrhifera.

M. tuberculosa (tubercled).—­This is a very pretty and distinct plant, of recent introduction, and easily cultivated.  It has a central stem, 6 in. high by 2 in. in diameter, conical in shape, and surrounded at the base by globose branches or offsets.  The tubercles are closely set in numerous spiral rows, and are 1/2 in. long, rather narrow, pointed, with a crown of radial spines, very slender, hair-like, white, and 1/2 in. long; central spines three or four, 1/2 in. long.  At the base of each tubercle is a pea-like tuft of white wool.  In this kind the spines fall from the old tubercles, which are persistent, gradually hardening to a cork-like substance.  The flowers are produced in the apex of the stem, and are 1 in. long and wide, daisy-like, pale purple in colour; they are succeeded by red, oval berries, which are as pretty as the flowers.  About five flowers are developed on each stem annually—­May and June.  Native of Mexico, in the mountains.  It thrives when grown in an ordinary greenhouse, on a shelf, in full sunshine.

M. turbinata (top-shaped); Bot.  Mag. 3984.—­Stem globose, depressed at top, about 3 in. in diameter, pale glaucous-green; tubercles quadrangular, flattened at the apex, and bearing, when young, from three to five erect, slender, hair-like spines, which fall off soon after the tubercles ripen, exposing little depressions or umbilica, and giving the stem a bald, pudding-like appearance, quite distinct from any other kind.  Flowers from the centre of the stem, short, about 1 in. across, pale yellow, with a reddish tint outside; anthers yellow.  Two or three flowers are usually expanded together in the month of June.  Native country, Mexico.

M. uncinata (hooked).—­Stem globose, simple, about 4 in. in diameter; tubercles closely pressed against each other at the base, where they are four-angled; in length they are 1/4 in., and they are blue-green in colour.  Apex bearing four short spines, arranged crosswise, and 1/4 in. long; central spine slightly longer, yellow, and hooked.  The flowers are 1 in. long and wide, erect, the tube hidden by the young mammae, amongst which they appear in May and June; they are purple in colour, a line of deeper tint running down the middle of each petal.  Like all the kinds with short, angular tubercles, this species is easily managed, flowers freely and profusely, and always ripens seeds.  Native of Mexico.  It may be grown in a frame, or even out of doors, all through the summer, removing it to a greenhouse for the winter.