抄録
The position of the formation of "stunted roots" within a hill of rice plants was examined, using samples taken from 6 different paddy fields at Sakata City, Yamagata Prefecture. "Stunted roots" were found to occur rather abundantly in the following position within a hill; 1) in the higher "shoot-units" of each stem, 2) in the upper parts within a "shoot-unit", 3) in the central stems of a hill, as compared with the peripheral ones, and 4) in the stem parts where another tiller is in contact with. The number of "stunted roots" as well as the percentage of the number of the total differ markedly according to the growing conditions of the plants examined. The plants taken from 6 different paddy fields were thus divided into two groups, A and B. The group A is characterized by the abundant "stunted root" formation, with relatively more "stunted roots" at the middle "shoot-units" along the stems. In the B group, on the contrary, "stunted roots" were less in number, however, the number increased towards the higher "shoot-units". The plants belonging to the group A were found, as compared with those of the group B, to receive more nitrogenous chemical fertilizer as basal and top dressing. Some possible mechanisms underlying the "stunted root" formation were discussed in relation to their position. Those are 1) the competition of assimilates during the later stages of the plant development, 2) the mechanical stress exerted by crowding together of many stems, 3) the changes of nutritional status brought about by the excess nitrogen application, and so on.
