核桃雌雄同株,雌雄花期不一,有的树雌花先开,有的树雄花先开。1973年我们在洛南县白洛、石门调查了284株,其中雄花先开的占36.6％,雌花先开的占61.6％。因此,坚果的绝大多数为天然的株间杂交种,实生繁殖后,个体间差异很大。运用单株选择的方法,选出优树,通过嫁接繁殖,提高产量和质量,是目前国内外实现良种化的主要途径之一。法国从100～150个品种中选了7个主要品种,“福兰克蒂”占80％ ;美国主要发展4个品种,其他各国趋向亦是如此。我国在选择优树和优良品种方面也作了许多工作:一是把坚果性状比较接近的个体划分为不同的类型(过去称为品种),山西省选出68个,我省1960年评选出151个,新疆选出7个,云南15个。这些都对当时的核桃良种化起到了一定的促进作用,但因多为实生繁殖,不能形成遗传性状稳定的真 Walnut androgyny, different male and female florescence, some tree female flower first open, some tree male flower first open. In 1973, we investigated 284 strains of Bailuo and Shihmen in Luonan County, of which 36.6% were male and female, and 61.6% female and first opened. Therefore, the overwhelming majority of nuts are natural inter-strain hybrids that, after their reproduction, vary widely among individuals. It is one of the main ways to achieve thoroughbred planting at home and abroad by using single plant selection method, selecting superior tree, and propagating through grafting to improve yield and quality. France selected seven major cultivars from 100-150 varieties, while Frantiquetia accounted for 80%. The United States mainly developed four varieties, as did other countries. China has also done a lot of work in selecting excellent trees and fine varieties: one is to divide the individuals with similar nut traits into different types (formerly known as breeds), 68 in Shanxi Province, and 151 in 1960 A, Xinjiang elected 7, Yunnan 15. All of these played a certain role in promoting the seed quality of walnut at the time, but because of the mostly real-life reproduction, it is impossible to form a stable genetic trait