Abstract
The correlations were examined between the growrth angles of crown roots to the soil surface and their diameters in rice plants. 1. A significant correlation was observed between the growth angles and the root diameters, when the whole crown roots of a hill were treated collectively. Namely the thicker roots tended to grow vertically, while the thinner ones horizontally. Thecorrelation coefficient, however, was not always high. The same relationships were found when the crown roots were examined among the upper, the lower or the "P shootunit" roots, respectively. 2. Highly close correlations were found between the growth angles and the root diameters when the crown roots were grouped according to their time of emergence in the vegetative phase of the plants. Their relations, however, fell into different regression lines in accordance with the growing stages of the plants. As to the crown roots emerged after the plants entered into the reproductive phase, no such correlations were found. As a result, it is considered that a possible relation may exist between the geotropism of crown root and their diameters. Further, the geotropism may be affected by the varying quantity of assimilates translocated from the shoot during the growing stages of the plants.
