callus, the white, formless tissue that grows from cambium tissue at cut and wounded surfaces of the grapevine on stems and roots. It is critical for vine grafting since it signifies that the conditions for cell division are favourable and that the underlying graft or bud has united. High humidity, oxygen supply, and warm temperatures are the major requirements for rapid callus development. In the field, these conditions may be achieved by waxing or by wrapping the tissues tightly with plastic grafting tape. After bench grafting, the cuttings are packed with moist material and held in a warm, humid room. (See also tissue culture and illustration under grafting.)
