抄録
By means of the "leaf-cutting" method, the development of lateral root primordia of rice plants was investigated in relation to the diameter as well as the growth rate of crown roots on which they were formed. 1. The distance from the crown root tip to the youngest lateral root was variable among the crown roots examined. That is, the tip-to-lateral distance was greater in the thick and rapidly growing crown root than in the thin and slowly growing one. However, the time required for the development of each lateral root primordium was almost constant, irrespective of the diameter or the growth rate of its parent crown root (Figs. 4 and 5). 2. The lateral roots of rice plants have generally been divided into thick and thin group. The difference of their thickness was found to occur at a developmental stage, when each primordium reached 60-70 μm in length (Figs. 6 and 7). The stage coincided with the time when the primordium established its own organization with distinctive epidermis, cortex, stele and root cap (Fig. 8). Later, the thickness of each primordium increased and reached the maximum just before its emergence from the epidermis of the crown root (Fig. 7). 3. When the crown roots were decapitated, abundant thick laterals were formed in the remaining proximal portions. However, the primordia already aquiring their own organization mentioned above were not affected by the manipulation (Fig. 11). This suggests that a certain factor may determine the thickness of lateral roots during their early primordial stages.
