<正>通过对湿加松（湿地松×洪都拉斯加勒比松）家系间早晚生长性状的相关性研究表明，18个湿加松家系的树高、胸径、材积差异均极显著；各家系树高、胸径、材积的年度相关主要受遗传影响；造林后第2年的树高、第3年的胸径和材积估计造林后10a的材积均具有极显著的相关性，而且选择效率最高，表明湿加松家系在造林后2a可进行早期选择。湿加松早期选择的方法是：在2年生时根据树高生长量淘汰早期生长较差的家系，淘汰率为30%以内；在6年生时根据材积生长量选择生长最优的家系，入选率为35%r以内。

D, L-lactic acid was polymerized through melt polycondesation in order to prepare poly(lactic acid) with high optical properly. Polarimetry, FT-1R, DSC, 1H-and 13C-NMR were used to detect microstructure, molecular weight, and optical purity of poly (lactic acid) samples. Racemic PDLLA was prepared from D,L-lactic acid with Sn powder as catalyst or without catalyst. Both SnCl2/p-toluenesulfonic acid system and SnCl2/o-toluenesulfonic acid systern could be used as catalyst to obtain PDLLA with higher molecular weight(M,>20 000), lower dispersity (being 1. 1), and higher optical purity (70. 5%) due to excessive L-conformation units in polymer chain. Poly(lactic acid) with high optical purity prepared from D, L-lactic acid could effectively low the cost of poly(lctic acid) materials.