a little wool at the base.  The flowers are borne on the top of the stem, two or three of them together; the sepals are green and red, and the spreading petals are straw-coloured and glossy, their edges near the top being toothed.  In the centre of the shallow cup formed by the petals, and which measures nearly 4 in. across, the orange-coloured stamens are clustered, in a kind of disk, through the middle of which the yellow stigma projects.  It is a native of Mexico, at an altitude of 5000 ft.  Introduced in 1848, when it flowered at Kew, in June, at which time it flowers almost every year now.  A warm greenhouse affords the most suitable conditions for it; but, unless it is kept in full sunshine both summer and winter, and perfectly dry during the latter season, it will not produce any flowers.  As a flowering plant, it ranks amongst the very best of the Mamillarias.  It is easily propagated from seeds ripened on cultivated plants.

M. dasyacantha (thick-spined).—­Stem 2 in. to 3 in. high, almost globular, and covered with spiral whorls of tiny tubercles, in the grooves of which is a little whitish wool, which falls away as the tubercles ripen.  The spines upon the tubercles are arranged in little stars, with an erect central one.  The flowers are small, and spring from the centre of the stem.  This is one of the Thimble Cactuses, and is too small to have any great attractions, either in stem or flowers.  It is, however, a pretty plant, especially when studded with its ruby-like flowers, which look like coloured Daisies growing upon a dense tuft of hairs.  It is a native of Mexico, where it grows on high mountains among short grass and other herbage.

M. discolor (spines two-coloured).—­Stem globose, about 4 in. in diameter; tubercles smooth, egg-shaped, their bases embedded in white wool, their tips crowned with stellate tufts of short, reddish spines.  Flowers numerous, and borne from almost all parts of the stem, less than 1 in. wide, and composed of a single whorl of narrow, reflexed, rose-purple petals, surrounding a large, disk-like cluster of yellow stamens.  The flowers are so short that they are half hidden by the tubercles.  It is a native of Mexico, where it grows on rocks, in warm, sheltered places.  Under cultivation it thrives when grown on a dry shelf in a warm house, and kept moist in summer, but perfectly dry in winter.

M. dolichocentra (long-spurred); Fig. 58.—­Apparently this is a variable species; at all events, plants of widely different habit are found under this name, one of them represented in the Figure here, another in the Garden, Vol.  XVII., whilst others are figured or described in other books.  What is known at Kew as the true plant is that here figured.  This has a stout stem, about 8 in. high and 3 in. wide, and covered with smooth cone-shaped mammae, with woolly bases and stellate tufts of spines on their tips.  The flowers are produced about 1 in. from the top of the stem, and are less than 1 in. wide; they are,