Abstract: Branch-trunk junctions is an important part of tree's structure and function, which contains branch, the base of the branch involved in the xylem of trunk in the growth of the trunk, and also the knot formed after the branch was removed from the trunk. However, because of the negative impacts on the performance of the product, the research and utilization of the branch-trunk junctions is limited. With the development of bionics, the branch-trunk junctions have been gradually attracted great attention from scholars at home and abroad and related colleagues because of its complex structure, orderly connection and high toughness, decay resistance and other biological characteristics, and also as a kind of excellent biological composite materials. Many studies show that the branch-trunk junctions contain many artificial materials incomparable functions of intelligent composite material and structure characteristics. The deep research on branch-trunk junctions structure and its performance is expected to break its past use of limited territory and develop new application areas, and may also provide a new type of bionic research and development of high performance material beneficial enlightenment and the scientific basis. This paper summarizes the current research status of the structure and properties of the branch-trunk junctions from four fields,those are, the structure, chemical extraction, physical and mechanical properties. First of all, the structural characteristics at the level of macro observation and the intelligent adaptive performances changing with the external environments were respectivdy expounded. Secondly, the protective efficacy of the chemical extraction of knot was mainly summarized from the effects of chemical extracts on forest antisepticision and forest natural pruning. Then, the comparative studies of the branch-trunk junctions and tree stem in dry density, shrinkage properties and the change rule of physics were summarized. The related research on the correlations between mechanical properties and matrix material, and between structure arrangement and functional properties, and stress distribution characteristics was finally summarized. At the same time, this paper also describes examples of bionic engineering materials and structures and related branch-trunk junctions, as well as the related research providing some inspiration for the bionic design. In view of the complexity and particularity of branch-trunk junctions, the present studies on wood structure and properties of branch-trunk junctions awareness is relatively weak, and the research reports about branch-trunk junctions cell level fine structure and main chemical composition and the physical and mechanical properties is relatively less and not thorough. Based on these, the author research on wood structure and properties of branch-trunk junctions in the former, the paper brings forward several suggestions about further research on the wood material side of bionics, including those:1) Strengthening the macro and micro level of each branch-trunk junctions wood structural features and adaptive mechanisms of regulation. 2) Exploring the minor cellulose, hemicellulose and lignin and extracts and other chemical components and micro distribution mechanism of synergistic effect on the function of trees. 3) Carrying out branches, knots and parts of the trunk density, moisture variation and internal relationship of connection. 4) Exploreing the fine structure parameters on the branch-trunk junctions of wood physical and mechanical properties of the self adaptive control mechanisms, building the mathematical model of branch-trunk junctions fine structure and chemical composition of the wood structure parameters between physical and mechanical properties.

Key words: branch-trunk junctions, wood, structure, properties, bionic science