Distribution of polysaccharides and their changes in quantity in shoot apez of a light-sensitive varity, Rikuu No. 20, during the morphogenesis of foliar and floral primordia were investigated by means of “PAS” reaction. Thei purpose of thie study was to get some information about the role of polysaccharides in the physiological process of flower bud differentiation. Throughout the stages of vegetative growth a large amount of polysaccharides was always observed to deposit in node, internode and pith, showing the highest concentration in node. However, when examined closely, they aer confirmed todistrbute as for as in cambium-like zone which situates in the opposite side of the yougest loaf primordium. Such is the localization and the concentration gradient of polyaccharides in shoot apez in the rice plant in its vegetative growth stage. The same localization of polysaccharides is also observed in the early stage of generative growth when whoor apex has already changed into a young ear. As the vegetative growth approaches its end, concentration of polysaccharides in the region of shoot apex increases gradually and reaches their maximum amount in the stage just before the ear differentiation. However, when the differentiation starts, their concentration in the region decreases rapidly. The situation observed here shows that the process in essentially the same in bothe the vegetative and generative development in so for as polysaccharides deposit first in the tissue having meristematic potentiality and then organogenesis follows. From the facts it is easily approved that polysaccharides play an important role in supplying necessary energy and in synthisizing proteins for the prganogenesis that follows. However, to make the inceptive cause of organogenesis flear it is necessary to investigate closely the behavior of proteins in the site of shoot apez during the critical period in which transition from the vegetative to the generative growth occurs, which will be dealt with in the second report.Some reference to the physiological cause of promotion of earing under short-day treatment of the light-sensitive variety, Rikuu No. 20, was made. It has been pointed out that less deposition of polysaccharides in shoot apex in such a variety under short-day than under normal conditions is taken to have an important bearing on the inception of generative organagenesis.