The spawn is the mycelium of the fungus held in a mass or "brick" of earth and manure. Various methods are employed for making the spawn, but the essentials of them all are that the body of the brick shall be composed of a porous and light material, which can be compressed into a compact mass; fresh mycelium must be communicated to this mass, and then a mild heat must be applied, until the whole mass is permeated by the mycelium. The mass should be kept in heat until the whole of it assumes a somewhat cloudy look, but not until the threads of the mycelium can be seen. Ordinarily, fresh horse manure, cow manure and good loam are mixed together in about equal proportions, enough water being added to render the material of the consistency of mortar. It is then spread upon the floor or in large vats, until sufficiently dry to be cut into bricks. When these are tolerably well dried, mycelium from a mushroom bed or from other bricks is inserted in the side of each brick. A bit of spawn about the size of a small walnut is thus inserted, and the hole is plugged up. The bricks are now placed in a mild covered hot-bed, with a bottom heat of 55° to 65°, and left there until the clouded appearance indicates that the mycelium has extended throughout the mass. Soil from a good mushroom bed is sometimes used to sow new beds, in place of commercial spawn. Old clumps of mushrooms may be allowed to become dry, and they may then be mixed into a bed. The spores will then stock the soil and produce a new crop. The full-grown mushroom may be laid upon white paper until the spores are discharged, and these spores may then be mixed into the earth. Propagation by spores is little understood, however. (See page 24.) =Mustard= (_Brassica_ or _Sinapis_ species). Propagated by seeds. =Mutisia.= _Compositæ._ Seeds. Layers and cuttings of growing wood, those of the tender species in bottom heat. =Mygindia=, Rhacoma. _Celastrineæ._ Seeds. Cuttings of firm shoots under glass. =Myoporum.= _Myoporineæ._ Seeds, when obtainable. Usually by cuttings of young wood in heat. =Myosotis= (Forget-me-not). _Boragineæ._ Propagated by seeds sown in spring in-doors or in the garden. The perennials may also be increased by divisions, in spring, or by cuttings placed under a hand-glass in a shady spot, in summer. =Myrica= (Bayberry, Sweet Gale, Wax Myrtle, Candleberry). _Myricaceæ._ Hardy species mostly by seeds, from which the pulp has been removed. Sow as soon as ripe, or stratify them. Layers and divisions may also be employed. The greenhouse species are increased mostly by green cuttings. =Myristica= (Nutmeg). _Myristiceæ._ May be increased by seeds; or by cuttings of ripened shoots placed in sand under glass, in bottom heat. =Myrobolan.= See Prunus.