LAYERING is an operation by which the propagation of plants is effected by laying down or bending the shoots, so that a portion of them can be covered with earth. A shoot so operated on is called a layer, and the point which furnishes the layers bears the name of stool. Some plants are so much disposed to emit roots that if their branches happen to come in contact with the earth they immediately begin to strike. But although it may be easily imagined that the obriervation of this common circumstance has led to the artificial practice, yet some additional operations besides that of merely bringing a shoot in contact with the earth are found necessary for many plants on which this mode of propagation is practised. Tho principle by which the operation is rendered effectual for the object in view is the following :—When the shoot of a freely disposed to send forth roots has merely its bent part.insertcd in the earth, the woody matter organised by the leaves passes down to tho roots nearly as usual; but if the communication along the alburnum is interrupted by an acute bend, twist, or incision, a callus will be formed, from which by degrees spongioles are emitted, and thus roots ultimately produced. A common error is to bury the layer too deep in tho earth ; for trees and shrubs, the depth should be front three to six inches, and the shoots of the previous season are the best fitted for the operation, the incision being made immediately under a bud or joint.
The part of the shoot intended to form a layer should be divested of leaves where it is to be covered with the mould, and a alit should be made on the bent part, or the branch should be twisted half round at the bend so as to disarrange the woody tissue, or the bark should be half or three-quarters ringed : the top of the shoot being bent gently upwards in order to give the plant an upright tendency in its after growth, while at the same time that position keeps the incision from closing; the branch is then fixed down by pegs or hooked sticks, cut down to within an inch or so of the ground, and covered with good mould, which should have been previously well stirred, and afterwards be kept tolerably moist. In general roots are emitted
in a few weeks, and by the end of a semen voting plants are obtained quite fit hs transplantation. Some plants 'however require to be left for two years on the stools before they are removed, and there are some which can hardly be male to root at all in this manner.
Planta so situated as to render it impossible to bend their branches to the ground may nevertheless be layered by having their shoots Introduced into a pot or box of soil elevated to them, and supported in a convenient position. This is h common practice among the Chinese, who cause branches of trees to root in this manner by partially ringing them, and covering the parts so ringed with a ball of clay, which is kept moist.