The CaCl₂-tube method for measuring the rate of transpiration.

Abstract

Some experiments were conducted on the method for measuring transpiration by the moisture absorption of granular CaCl₂. Following the results of preliminary test, the degree of moisture absorption was limited within ten per cent bf the dry weight or a quarter of maximum absorption to hold the error due to free-pass-moisture less than one per cent. On the comparison of the evaporation from a evaporative pan and the absorption by this method, any significant difference was not found at 95 per cent confidence level, and it was concluded that this method was accurate enough for practical use. As the rate of transpiration varies considerably with air velocity, the velocity at the leaf surface was fixed at a value between 1 to 2 cm per second. The distribution of transpiration by the leaves on various ous positions of the stem was shown. A leaf chamber was devised for measuring the partial transpiration in a leaf. The rate of transpiration from the upper and lower surfaces of a leaf was measured separarely. The difference was also shown on the rate of transpiration from the apical and basal parts of a leaf-blade.