Abstract: Based on the cotyledon node zone (CNZ) theory, the anatomical study on primary vascular system at seedling stage of Catalpa ovata. The results indicate that the CNZ of C.ovata is longer, and belongs to basipetal shifting type. From top to bottem, it has pith in the whole CNZ. There is mesarch tetrarch siphonostele in the lower portion of the CNZ, which divides into two parts from protoxylem in the middle portion of the CNZ and gradually form stele structure with eight collateral bundles. In the upper portion of the CNZ, two vascular bundles which formed shorter axile divide into three parts respectively and shape the model of eustele, then connect with endarch eustele of epicotyl. There are three-trace cotyledonary node in the seedling.

Key words: Catalpa ovata, seedling, primary vascular system, cotyledon node zone, basipetal shifting type