The particular method of making the cutting and the treatment to which it should be subjected, must be determined for each species or genus. Some plants, as many maples, can be propagated from wood two or three years old, but in most cases the wood of the previous or present season's growth is required. Nearly all soft and loose wooded plants grow readily from hard-wood cuttings, while those with dense wood are often multiplied more easily from soft or growing wood. Some plants, as oaks and hickories, are propagated from cuttings of any description only with great difficulty. It is probable, however, that all plants can be multiplied by cuttings if properly treated. It often happens that one or two species of a closely defined genus will propagate readily from cuttings while the other species will not, so that the propagator comes to learn by experience that different treatment is profitable for very closely related plants. For instance, most of the viburnums are propagated from layers in commercial establishments, but _V. plicatum_ is grown extensively from cuttings. =Particular Methods--Kinds of Cuttings.=--Cuttings are made from all parts of the plant. In its lowest terms, cuttage is a division of the plant itself into two or more nearly equal parts, as in the division of crowns of rhubarb, dicentra, and most other plants which tend to form broad masses or stools. This species of cuttage is at times indistinguishable from separation, as in the dividing of lily bulbs (page 25), and at other times it is essentially the same as layerage, as in the dividing of stools which have arisen from suckers or layers. This breaking or cutting up of the plants into two or more large parts which are already rooted is technically known as _division_. It is only necessary, in dividing plants, to see that one or more buds or shoots remain upon the portions, and these portions are then treated in the same manner as independent mature plants; or sometimes, when the divisions are small and weak, they may be handled for a time in a frame or forcing-house in the same manner as ordinary cuttings. Cuttings proper may be divided into four general classes: 1, of tubers; 2, of roots and root-stocks; 3, of stems; 4, of leaves.