The headquarters of the genus Mamillaria is Mexico, and the countries immediately to the north, a few being scattered over the West Indies, Bolivia, Brazil, and Chili.  Many of them grow on mountains where the temperature is moderate, but where the sunlight is always intense.  Others are found on limestone or gravelly hills, among short herbage, or on grassy prairies.  A small silvery-spined kind has recently been found near the snow line in Chili.  M. vivipara is quite hardy in New York, as also are several other kinds, whilst we learn that by planting them out in summer, and protecting them by means of a frame from heavy rain, dews, fogs, and sudden changes of weather, a good many species of both Mamillaria and Echinocactus are successfully managed in the neighbourhood of that town.

Cultivation.—­Particulars with respect to cultivation are given along with the descriptions of most of the species, but a few general principles may here be noted.  With only a few exceptions, all the cultivated Mamillarias may be grown in a warm, sunny greenhouse, or they may be placed in a frame with a south aspect, during our summer, removing them into artificially heated quarters for the winter.  They do not like a large body of soil about their roots, but always thrive best when in comparatively small pots.  If a sweet, new, fibry loam, mixed with broken bricks or cinders, be used to pot these plants in, they may then be left undisturbed at the root for several years.  Much harm is often done to the more delicate kinds of Cactuses by repotting them annually; the best-managed collection I have seen had not been repotted for four years.  This would not be safe if a poor and exhausted soil were used in the first instance.  The pots should be well drained with crocks, and these covered with a layer of fibre sifted from loam.  In summer, the soil should be kept moist, but never saturated; and after a bright warm day, the stems may be moistened over by syringing them with tepid water.  A point of much importance in connection with these, and indeed all tropical and extra-tropical plants, is, that the water used for watering or syringing them should be rain-water if possible, and never more than a degree or so colder than the plants themselves would be.  Thus, a plant which had been standing in the full glare of a midsummer sun all day, would be much endangered by watering it with cold tap-water.  Where proper arrangements for water are not made in a greenhouse or stove, it is a good plan to place the water wanted for the day’s use in the sun along with the plants.  A little bag filled with soot and tightly tied at the neck, and water, is a good method for rendering hard tap-water suitable for watering the roots of plants.  In winter, Mamillarias may be kept quite dry at the roots, except in mild sunny weather, when a little water may be given.

A collection of the most distinct kinds may be successfully managed in a glass case in a room window, providing the sun shines through it for a few hours in the day.