The development of primary vascular tissues of root-stem transitional region was studied in Robinia pseudoacacia L. seedlings of 1-12 days using sequential paraffin section. The primary vascular tissues of roots are connected with the cotyledons via the hypocotyl. The results support the viewpoints of Esau et al. that the whole seedling of Robinia pseudoacacia L. is divided into two systems of the root-hypocotyl-cotyledon and the epicotyl, and there is only a simple linkage between the vascular tissues of stem and the hypocotyl without any transition.