人们已经开始有计划地改良美国东南部的美国梧桐(Platanus occidentalis L.)。在美国梧桐改良计划中,选择起主要的作用。决定对哪些性状进行选择,选择强度多大,采用何种选择方式以及如何进行早期选择,都是要讨论的主要内容,这些因素影响到改良计划的成败及计划能否进行下去。在大多数美国梧桐的研究中,人们发现生长性状(树高、直径、材积和单株干重) People have begun to systematically improve Platanus occidentalis L. in the southeastern United States. In the sycamore improvement program, choose to play a major role. Determining which traits to choose, how strongly to choose, how to choose and how to make early choices are the main topics to be discussed. These factors affect the success or failure of the improvement plan and whether the plan can be implemented. In most Sycamore studies, growth traits (tree height, diameter, volume, and dry weight per plant)