This experiment was conducted for investigation of the varietal difference of the physiological activity of the root and its relation to the growth of rice plant between a Japanese variety Norin No. 29 and a Korean variety Nongkwang. These rice plants were cultured in the normal soil (Konosu soil), humus-rich soil (Matsuo soil) and poor sandy soil (Oami soil). From the experimental result, the following varietal differences were found under the reduced humus-rich soil condition. 1. At tillering stage, the physiological root activity of Japanese variety Norin No. 29 tended to be higher than that of Korean variety Nongkwang. But at ear-formation stage, Nongkwang showed much higher root activity than Norin No. 29 under reduced condition. 2. The formation of silicicated epidermal cell of top leaf blade tended to be more influenced by reduction of soil than by the content of available silica of soils. The above cells were found to be more in top leaf blade of Nongkwang than in Norin No. 29. 3. The degeneration of spikelets was assumed to be caused by reduced condition in humus-rich soil. In this soil, the decrease in the number of spikelets of Norin No. 29 tended to be higher than that of Nongkwang.