抄録
The growing direction of rice roots and their geotropic responses were examined using the "leaf-cutting method), i.e. a method of culturing one or more "shoot units" of a stem in water or agar media, thus making the direct observation of the growth of the emerging crown roots possible. The results obtained were as follows: All the upper roots of each "shoot unit" grew horizontally, and the lower ones in various directions, while those of the prophyll "shoot unit" located at the base of each tiller grew vertically, irrespective of the position of the tillers on the parent stems. Among the lowcr roots of each "shoot unit", those which emerged in the vegetative phase of the plants grew obliquely-downwards or vertically, while those emerged after the panicle initiation stage of the plants grew horizontally. These findings coincides with those obtained previously in the field or pot cultured plants. The experiments of laying sideways of the culture vessels, while roots were growing in agar media, revealed that the roots originally growing more vertical responded more to the newly imposed geotropic stimuli. These results mentioned above suggest that the rice crown roots are endowed with a specific geotropic responsiveness which is determined by the positions on stems on which they appear.
