核桃、板栗、苹果等果树中的大部分品种,自花结实率很低,一般须经异花授粉才能结实。因而,核桃、板栗、苹果的种子,实际上皆为天然杂交种,在用种子繁殖果树时,实生的后代与其母本(或父本)比较,有明显的分离─—变异现象。在果树上通称为实生变异,为了保持果树品种的优良性状,苹 Walnuts, chestnuts, apples and other fruit trees in most varieties, self-fertility rate is very low, usually cross-pollination to be strong. Therefore, the seeds of walnuts, chestnuts, and apples are actually all natural hybrids. When the fruit trees are bred with seeds, the progeny of the actual generation have obvious separation-mutation phenomena compared with their parent (or father). Commonly known in the fruit tree as a real mutation, in order to maintain the fine traits of fruit trees, apple