The relationship between the number of primary roots and yield components was investigated by using 16 hills of rice plants grown on 4 different farmers' paddy fields. The data obtained were analyzed statistically on per-hill or per-plant basis. Throughout the analyses on both per-hill and per-plant basis, a high correlation was observed between the number of spikelets and the weight of ripend kernels, both of which were closely related to the number of primary roots. However, no notable variation was found either in the percentage of ripened kernel or in the thousand-kernel-weight. In the case of analyses per hill, the number of elongated primary roots showed a close correlation with the number of spikelets and the weight of ripened kernels. In contrast, the total number of primary roots as well as the number of 'stunted' primary roots did not show any relation with either of the yield components mentioned above. In the case of analyses per plant, close correlations were noted among most characters examined. These phenomena within a plant were attributed to the change in the number of culms, which were highly correlated with most of the other characters. When the partial correlations were examined by fixing the number of culms, the total number of primary roots and the number of elongated primary roots were the characters that exclusivery showed significant correlations with the number of spikelets or with the weight of ripened kernels. From the above investigations, it was assumed that among the primary roots, the elongated roots may have the utmost intimate relationship with the yield of rice plants.
