almost purple just before fading.  Flowering season, August.  Native of Mexico, where it is found in loose, sand on hillocks, generally about the roots of Acacias.  It is one of the most beautiful of all Mamillarias; but it is, as yet, rare in collections.  It requires the same treatment as M. longimamma, except that, owing to the woody nature of its rootstock, and its long, tap-like roots, it should be planted in pans instead of pots, using a compost of rough loam, mixed with lumps of broken brick or limestone.

[Illustration:  Fig. 64.  Mamillaria macromeris.]

M. macrothele (large-nippled); Bot.  Mag. 3634, as M. Lehmanni.—­This belongs to the same group as M. cirrhifera, but is distinguished by its large mammae, which are four-angled at the base, 3/4 in. long, narrowed to a point, upon which is a tuft of wool and a cluster of about eight spines, 1/2 in. long, spreading, reddish-brown in colour, the central one being almost black, 1 in. long, and pointing downwards.  In the axils of the mammae are tufts of white wool.  Flowers on the top of the stern, erect, spreading, about 11/2 in. across when expanded; the petals overlapping, and pale yellow; the stamens red at the base, arranged in a dense cluster, and the rays of the stigma spreading over them.  Flowering time, early summer.  Native country, Mexico, on prairie lands, at high elevations.  This species is almost hardy in the warmer parts of this country, suffering from damp rather than frost in winter.  The stem is not particularly handsome, but the flowers are large and bright, and they are produced annually by plants which are grown in a cool, well-aired greenhouse or frame, with the sun shining on them all day.

M. micromeris (small-flowered); Fig. 65.—­A small, cushion-like plant, with a stem never more than 11/2 in. across by about 1 in. in height, so that it has the appearance of a small, flattened ball, with a raised, disk-like portion on the top.  The mammae are very small, and they are completely hidden by the numerous fine, white, silky spines and wool which spring in tufts from the apex of each mamma, and interlace so as to form a spider-web-like net all over the stem.  The flowers are small, and they spring from the centre of the disk-like top of the stern; they are composed of from three to five sepals, and five petals, which are whitish or pink, and measure about 1/4 in. across when open.  Native country, Mexico, where it is found only in naked places on mountain tops or sides where limestone is plentiful.  It requires much care under cultivation, water in excess being fatal to it, and a soil of the wrong sort soon killing all its roots.  It is cultivated at Kew in a small pot, in a mixture of loam and lime rubbish, and grown in a warm greenhouse.

[Illustration:  Fig. 65.  Mamillaria micromeris.]