The differentiations of vascular bundles in the leaves, stems and panicles of rice plants were observed, and the differences between the vegetative and reproductive periods were studied. In general, when a leaf primordium covers on the shoot apex, the main vascular strand differentiates at the base of the leaf primordium and grows acropetally and basipetally, but the lateral vascular bundles proceed always acropetally. Each of the primary branches of panicles has a large vascular strand, which has differentiated at the each base of the primary branch primordium, and its differentiating aspect resembles closely to the case of the main vascular strand in the leaf. Then, the large vascular strands in the primary branches of panicles and the main vascular strands in the leaves are presumed to be homogenous tissues. Accordingly, it can be recognized that through the whole growth periods of rice plants, when a protuberance which differentiates on the shoot apex grows to a certain magnitude, a large vascular strand differentiates at the base of the protuberance. Therefore, the differences of patterns of vascular strands between the stem and panicle depend on the different patterns of the protuberances grown on the shoot apices in the vegetative and reproductive periods.