Studies on the relation between soil moisture and growth of tobacco plant. : 2. On the change of the rate of transpiration per unit leaf area.

Abstract

1. The rate of transpiration per unit leaf area of the 9, 11, 13, and 15 th leaf of the tobacco plant was measured seven times respectively, during the stage from the leaf length of about 10 cm to after the final length attained. It was demonstrated that the transpiration rate per unit leaf area, measured on the leaves of every stem position, showed a convex curve having a peak at the time when the leaf area reached about 30 per cent and the leaf length about 60 per cent of the final size. 2. The transpiration rate per plant estimated from the above mentioned curves and the lengths of all leaves, showed a convex curve. On the other hand, the transpiration rate per unit leaf area calculated from that of per plant showed a decrement curve, This corresponded to the result cited in the previous report. Therefore, the cause that the peak of the transpiration rate per unit leaf area appeared at considerably early stage was proved to be due to the fact that the peak of the transpiration rate in each leaf on a plant appeared at earlier stage in the elongation of each leaf. 3. The transpiration rate from the three leaves, the largest leaf and adjacent upper and lower leaves, occupied 80 to 50 per cent of the total transpiration rate per plant and this ratio decreased with the growth of the plant accompanied by the increment of the number of leaves. The transpiration rate was generally remarkable in the leaves developing rapidly.