Abstract
The secondary roots of tobacco seedlings were grown in the water media to which gases of air, oxygen, nitrogen or mixtures of oxygen and nitrogen were bubbled. The results obtained were as follows: 1. The elongation of root was increased in accordance with the root growth. The frequency of cell division in the meristem was most flourishing in the root 2--30 mm in length, on the other hand, the degree of cell elongation was most conspicious in the root elongated beyond 40 mm in length. 2. In the O2-sufficient water media, many lateral roots developed from all length of the root, whereas in the O2-deficient media, the development of the laterals were restricted to upper part. 3. The optimum concentration of O2 for root elongation was around 9 ppm and in such a concentration the elongation persisted for long period, but in the media of 1 ppm the elongation was restricted. 4. In the seedlings grown on the O2-sufficient water media, cutting off of leaves affected the root elongation, the recorded data on the O2-deficient media did not show such a response. 5. pre-treatment of the seedling with O2-deficient media restricted the elongation of root in comparison to the treatment with O2-sufficient one. The reason would be reduced to the fact that both cell division and cell elongation in the root tip were strongly affected by the influence of O2.
