1. This experiment was made to determine of the influence of water depth upon the growth of tillering primordium and tillering bud of rice seedlings. 2. The degrees of water depth used were three, 0 cm (saturated condition in the soil) 3.0 cm and 5.0 cm. 3. The first tillering primordium grew to about 0.5∼0.8 mm in length and 0.3∼0.4 mm in width, but after then it stopped to grow. It was rare to grow to more than 1.0 mm. However, at 0 cm, the growth was good and at 3.0 cm and 5.0 cm they become bad respectively. 4. The second tillering primordium and tillering bud received a great influence in its growth by the water depth, and it was best at 0 cm and flooded condition of 5.0 cm showed the marked inhibition of growth. There are two developments to the second tillering primordium, one which grows and appears outside of the leaf-sheath and one whose growth stops. It is judged that this variation comes from the adaptation or the non-adaptation of cultural environments. 5. In the third tillering primordium and tillering bud, up to the time of the appearing of the 4 th or 5 th main leaf the growth is most prominently at 0 cm and bad at 5.0 cm. At the appearance of the 6 th or 7 th main leaf the tendency of gradual decrease was observed between the different water depth. However at water depth of 5.0 cm some of which stop to grow. 6. In the fourth and fifth tillering primordium and tillering bud, the influence of water depth was not observed too much during the appearance of the 5 th or 6 th main leaf, but at the appearance of the 7 th or 8 th main leaf the tendency of improved growth was observed in the 3.0 cm and 5.0 cm when compared to 0 cm. 7. As to the width of the tillering primordium and tillering bud, we recognized the tendency that they grow in proportion to the length, but more slowly than the length.