<正>外来入侵物种对物种多样性产生的严重影响主要表现为排挤本地动植物，导致局部种群的消亡，造成局部高密度分布的稀有物种绝灭。外来入侵物种对遗传多样性的影响主要体现在：种群破碎化，导致遗传漂变和近亲交配；本地种与外来种杂交，造成遗传污染；局部野生、原始种群消失，导致遗传材料减少。在定性分析生物入侵对我国物种及遗传资源影响的基础上，笔者以政府有关部门统计数据和典型案例报道为主要信息源，评估了2000年生物入侵对物种的潜在保留价值和作物遗传资源造成的直接经济损失。结果表明：生物入侵对我国物种资源和作物遗传资源造成的经济损失分别为7104.14万元和11028.4万元。

The experiment aimed at observing the origin and development of somatic embryos of Liriodendron chinense × L. tulipifera by scanning 6lectron microscopy. The results showed that the structure differences between embryogenic callus and non-embryogenic callus were distinct. We found that the cells of embryogenic callus were often small and equal. There were cell masses consisting of many embrgogenic cells and had the shape of ball. While the cells of non-embryogenic callus were so big that they cannot form cell masses and there was interspace between them. The embryogenic cells can propagate rapidly and some of them formed the primitive cell of the somatic embryos. The plantlet regenerations were developed from global embryo, heart-shaped embryo, torpedo-shaped embryo and cotyledon embryo. The embryogenic tissue cultured from Liriodendron hybrids had a significant polarity and relative independence. The somatic embryo, especially the mature somatic embryo, would become incompact with embryogenic callus and fall off easily.