Difine grafting?

Grafting is a horticultural technique used to join parts from two or more plants so that they appear to grow as a single plant. In grafting, the upper part (scion) of one plant grows on the root system (rootstock) of another plant.

In grafting, one plant is selected for its roots, and this is called the stock or rootstock. The other plant is selected for its stems, leaves, flowers, or fruits and is called the scion. The scion contains the desired genes to be duplicated in future production by the stock/scion plant. For successful grafting to take place, the vascular cambium tissues of the stock and scion plants must be placed in contact with each other. Both tissues must be kept alive until the graft has taken, usually a period of a few weeks. Successful grafting requires that a vascular connection takes place between the two tissues.  

Grafting is most commonly used for the propagation of trees and shrubs grown commercially. Grafting is limited to dicots and gymnosperms.