Abstract: Adonis aestivalis belongs to Adonis of Ranunculaceae. Its seedling isapparently divided into three zones:epicotyl shoot zone, cotyledon nodezone (CNZ) and hypocotyl root zone. The seedling is with the center ofthe cotyledon-node-zone, the middle and upper parts of the CNZ upwardare cotyledon-node-stem transitional region and the hypocotyl of theseedling downward is cotyledon-node root transitional region. Some onto-genetic studies on the primary vascular system of seedlings of somegenera in Ranunculaceae have been reported. But the transformation of thecotyledon-node-stem transitional region of A. aestivalis is different fromthose of other genera in Ranunculaceae. The main difference is that itsmetaxylem develops tangentially to form undeveloped double-lip-likecollateral vascular bundles after the mesarch, diarch haplostele withdouble fan-like metaxylem reaches the middle part of the CNZ. Theparenchyma appears in the center of the haplostele and divelops furtherto form the pith. The upper part of the CNZ is divided into severalundeveloped endarch collateral vascular bundles which directly formeustele of the epicotyl. This study is to testify the CNZ theory and revealthe evolutional rules of primary vascular system in Angiosperms.

Key words: Adonis aestivalis, Seedling, primary yascular system, cotyledon node zone