Abstract
In order to find out a clue to diagnose the activity of rice roots, some experiments were conducted concerning the relation between the morphological and physiological characteristics of the root and its nutrient-absorption. The results of experients are as follows:- 1) Sprouting of new roots was most active at the stage of most vigorus tillering, declining thereafter with the advance of growing stage of the plant. And new roots were scarcely seen after heading. 2) The highest velocity of absorption of N, P2O5 or K2O, expressed as the maximum amount of each nutrient absorbed by the root in a day, was observed at about the same date at the time when root-sprouting becomes most active and the number of healthy root tips per plant becomes most abundant, while the highest velocity of absorption of FeO, MgO or SO3 and of SiO2 or MnO were observed 10 days and 20 days respectively after that of N, P2O5 or K2O (Fig. 3). 3) Absorption of NH4-N and P2O5 by excised roots was most active in new roots (Class I or I & II), than in old roots (Class III, IV), while that of MnO was rather active in older roots. 4) These facts as above seem to suggest that N, P2O5 or K2O is more vigorously absorbed by new roots than by old ones. 5) New roots, especially those belonging to class I, showed a high ability for absorption of N and P2O5, a high content of N, P2O5, a high respiratory rate and a high activity of cytochrome oxidase, indicating that an active respiration through the cytochrome-cytochrome oxidase system is responsible for the active absorption of these nutrients by new roots.
