This section is from the book "Commercial Gardening Vol1", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
This method of propagation may be called overhead layering. It consists in making an upward or circular slit in the stem of a plant that has become too tall or leggy. Some sphagnum moss and leaf mould is then tied round the wound, and is kept damp with the syringe every day.
In a short time the elaborated descending sap from the leaves develops a callus and a mass of roots through the moss. When a sufficient number of roots has been produced, the rooted head is severed and potted up. In this way tall Dracaenas, Crotons, Cordylines, Aralias, Ficus elastica, American Carnations, etc, may be propagated, as well as by other methods mentioned. If considered worth while, trees with branches too far from the ground might be propagated in this way, but the trouble would be to maintain moisture round the ringed portion. The sketch (fig. 69) shows how this method of propagation may be adopted for trees and shrubs, using a pot with a slit in one side for the purpose.
Fig. 68. - Stem Cutting of Thunia Marshalliana.
A, Old stem showing fibres from joints. B, Young shoot with roots at base (1/4 nat. size).
Fig. 69. - Aerial Layering.