[Illustration:  Fig. 67.  Mamillaria pectinata.]

M. phellosperma (corky-seeded).—­A pretty plant, resembling M. Grahami in all points except the seed, which, as is denoted by the name, is half enveloped in a corky covering, suggesting acorns.  Stems simple, sometimes proliferous at the base, globose when young, afterwards almost cylinder or pear-shaped, 5 in. high, 2 in. in diameter; tubercles 1/2 in. long, arranged in twelve spiral rows, slightly woolly in axils.  Spines radiating, in two rows, about fifty on each tubercle, the three or four central ones being hooked at the tips or sometimes straight; length, 1/2 in. to 11/2 in.  Flowers (only seen in the dried state) 1 in. long and wide.  Native of the dry gravelly hills and sand ridges in California and Colorado, and, therefore, requiring greenhouse treatment.  This plant is cultivated in the Kew collection, but it has not been known to flower there.  It is one of the most ornamental of the very spinous species, the radial spines being almost white, whilst the central ones are black, and look like tiny fish-hooks.  A large proportion of these Mamillarias are far more interesting in the form and arrangement of their tubercles and spines than in any floral character, and it is on this account that so many which are insignificant as flowering plants are included here.

M. pulchra (handsome).—­Stem globose when young and cylindrical when old, flattened at the top; height from 4 in. to 6 in.; tubercles large, egg-shaped, arranged in from eleven to thirteen spiral rows; spines in compact tufts, their bases set in whitish wool, irregular in length, and almost covering the whole of the stem.  Flowers medium in size, developed near the top of the stem from the woolly axils of the tubercles; colour bright rose.  Native of Mexico.  Flowering season, June.  Introduced in 1826.  A rare kind nowadays, though one of the prettiest.  It should always be grown in a warm house.  It has been also called M. pulcherrima.

M. pusilla (small).—­A tiny tufted plant, belonging to the group known as Thimble Cactuses.  It has stems 2 in. high; short, dark green tubercles, with tufts of whitish wool in the axils; spines thin and bristle-like, twisted, nearly 1 in. long, almost hiding the stem; they are whitish, with black tips.  The flowers are yellowish-white, with streaks of red.  Common in Mexico.  Flowering season, May.  It should be grown in a frame in summer, and wintered on a shelf in a warm greenhouse.  It would, no doubt, thrive in a window if kept in a sunny position and placed under a glass shade.  A variety known as texana differs in being more densely clothed with spines.  We have seen it grown into large clumps, covering a space 1 ft. in diameter, with dozens of erect little pyramids of whitish spines.