<正>针对短轮伐期桉树人工林林分冠幅生长的特点，在现实林分调查的基础上，模拟提出了适合有变点的短轮伐期桉树u6无性系林分冠幅生长阶跃函数模型。通过求解模型参数，分析了各参数的生物学意义。对树冠与林龄的回归分析结果表明：阶跃函数模型在具有变点的桉树林分树冠生长过程中的应用效果优于一般回归拟合模型，可较好地解决分段拟合模型在变点上的不连续问题。模型优化结果表明：在所有参与模拟的树冠生长的阶跃模型中，以幂函数模型为最优。

Differentiating from normal wood, baeterial of water drop shape, flake shape and lump shape are observed in pit membrane in wetwood of Abies lasiocarj pa (Hook) Nutt. (sub-alpine fir) using scanning electronic microscope. Not only ray parenchyma cells in wetwood are partially degraded but also margo strands in pit membranes are somewhat degraded by bacterial activities. Most of bordered-pit membranes in normal wood are un-aspirated at green condition and the proportions of aspirated pits in early wood and latewood are only 6.8% and 13.4% respectively. Nevertheless, most of bordered-pit membranes in wetwood are aspirated at green condition and the proportions of aspirated pits in early wood and latewood are at 77.7% and 72.1% respectively. The problem of hard-to-dry for sub-alpine fir could be reasoned from the considerable amount of aspirated pit membranes in wetwood.