The correct option is B Cambium
During grafting, a vascular connection takes place between the grafted tissues of stock and scion plants. The vascular cambium must be placed in contact with each other. The part selected for the role of roots is stock and the part selected for the stem is scion.This joining of vascular cambium makes grafting successful as it helps the continuous conduction of water, minerals, and food throughout the grafted plant. Thus the correct answer is option C.