Out-of-doors.—­There are some kinds which may be grown out of doors altogether, if planted on a sunny, sheltered position, on a rockery.  The most successful plan is that followed at Kew, where a collection of the hardier species is planted in a rockery composed of brick rubble and stones.  During summer the plants are exposed; but when cold weather and rains come, lights are placed permanently over the rockery, and in this way it is kept comparatively dry.  No fire-heat or protection of any other kind is used, and the vigorous growth, robust health, and floriferousness of the several species are proofs of the fitness of the treatment for this class of plants.

In any garden where a few square yards in a sunny, well-drained position can be afforded for a raised rockery, the hardy Cactuses may be easily managed.  To make a suitable rockery, proceed as follows:  Find a position against the south wall of a house, greenhouse, or shed, and against this wall construct a raised rockery of brick rubble, lime rubbish, stones (soft sandstone, if possible), and fibrous loam.  The rockery when finished should be, say, 4 ft. wide, and reach along the wall as far as required; the back of the rockery would extend about 2 ft. above the ground level, and fall towards the front.  Fix in the wall, 1 ft. or so above the rockery, a number of hooks at intervals all along, to hold in position lights sufficiently long to cover the rockery from the wall to the front, where they could be supported by short posts driven in the ground.  The lights should be removed during summer to some shed, and brought out for use on the approach of winter.  Treated in this manner, the following hardy species could not fail to be a success: 

Opuntia Rafinesquii and var. arkansana, O. vulgaris, O. brachyarthra, O. Picolominiana, O. missouriensis, O. humilis, Cereus Fendleri, C. Engelmanni, C. gonacanthus, C. phoeniceus, Echinocactus Simpsoni, E. Pentlandii, Mamillaria vivipara.

Having briefly pointed out the various positions in which Cactuses may be cultivated successfully, we will now proceed to treat in detail the various operations which are considered as being of more or less importance in their management.  These are potting, watering, and temperatures, after which propagation by means of seeds, cuttings, and grafting, hybridisation, seed saving, &c., and diseases and noxious insects will be treated upon.

Soil.—­The conditions in which plants grow naturally, are what we usually try to imitate for their cultivation artificially.  At all events, such is supposed to be theoretically right, however difficult we may often find it to be in practice.  Soil in some form or other is necessary to the healthy existence of all plants; and we know that the nature of the soil varies with that of the plants growing in it, or, in other words, certain soils are necessary to certain plants, whether in a state of nature or cultivated in gardens.  But, whilst admitting that