Correct Option: A

In grafting, union between stock and scion produces undifferentiated mass of cells called callus. Grafting is a method of plant propagation widely used in horticulture, where the tissues of one plant are encouraged to fuse with those of another. It is most commonly used for the propagation of trees and shrubs grown commercially. Grafting is limited to dicots and gymnosperms. Monocots lack the vascular cambium required.