白沙蒿种子萌发特性的研究 I. 粘液瘦果的结构和功能

白沙蒿(Artemisia sphaerocephala Krasch.)是中国西北部沙漠的流动及固定沙丘上广泛分布的优势种灌木。瘦果小而轻，借助显微镜和扫描电镜对瘦果的形态结构进行了观察，其种子的种皮与果皮愈合，果皮外层为很厚的粘液层，其粘液层在遇湿后迅速吸水膨胀，其重量增至原来的589倍。在自然生境中，粘液物质将沙粒粘附于瘦果的周围，使瘦果的重量发生变化。瘦果能长时间在水上漂浮，粘液物质有助于种子的萌发和苗的发育。白沙蒿产生三种不同颜色的瘦果，其种子具有不同的萌发速率但最终达到相同的萌发率。研究表明瘦果的粘液物质对白沙蒿种子的传播与萌发具有重要的生态意义。

SEED GERMINATION IN ARTEMISIA SPHAEROCEPHALA I. THE STRUCTURE AND FUNCTION OF THE MUCILAGINOUS ACHENE

Artemisia sphaerocephala Krasch. is a dominant shrub in large areas of active and stabilized sandy desert of northwest China. Achenes of A. sphaerocephala are very small and light. The morphology and structure of this achene was observed under a dissecting microscope and S.E.M. The seed coat and pericarp are concrescent while the outmost layers of the pericarp are covered by a layer which becomes mucilaginous when wetted and increases in weight 589 times by absorbing water. In the natural habitat, the mucilaginous layer holds sand particles to the achene thereby increasing the achene weight even further. These achenes can float on water for a long time, and the mucilage mass facilitates the seed germination and seedling development. A. sphaerocephala produces achenes in three colors that germinate at different rates but reach the same final germination percentages. We conclude that the mucilage layer of A. sphaerocephala achenes plays an important ecological function in seed dispersal and germination.