**3.1 Definition of distant graft**

Broadly speaking, grafting is that the branch or bud or stem of a plant is grafted onto the stem or root of another plant, so that the two parts coming from different plants are connected together and grow into a complete plant. Distant-grafting is that the grafting is carried out among different families/genus/species of plants.

The survived grafted plant, the whole scion and stock form a uniform conductive system, the stems and leaves developed by the scion and the root system of rootstock exchange for nutrient. Because the grafted plant is composed by two different individuals, where the roots of rootstock not only function to absorb water and minerals, but also function to synthesize organic acids and amino acids while the leaves of scion are the main organ for the synthesis of organic nutrients, both two parts are not mechanically combined but are an interdependent organic whole. Rootstock and scion each possess a specific function necessary for survival, and also affect the function of each other, including the synthesis of metabolites and the development of reproductive organs, which is consequently expressed in the progeny of scion seeds.
