核桃树在生长过程中,可分泌一种叫“核桃醌”的物质。它能抑制苹果树的正常生长,致使其长势弱,产量低,品质差。因此,核桃树不能靠近苹果园,更不能与苹果混栽。榆树在生长过程中也能分泌一种抑制葡萄生长发育的有害物质。这种分泌物接触葡萄或被葡萄吸收 Walnut tree in the growth process, can secrete a called “walnut quinone” material. It can inhibit the normal growth of apple trees, resulting in its weak growth, low yield, poor quality. Therefore, the walnut tree can not be close to the apple orchard, but can not be mixed with apples. Elm also secretes a harmful substance that inhibits the growth and development of the grape during its growth. This secretion comes into contact with the grapes or is absorbed by the grapes