The Daily March of Transpiring Power as Indicated by the Porometer and by Standardized Hygrometric Paper

Recent Work on Transpiration

“…This work thus gave results which are in full agreement with those of Livingston and Brown and of Mrs. Shreve (29). Trelease and Livingston (30), using the porometer method, found that the stomata continued to open after the transpiring power of the plant had reached a maximum for the day, and from this and their earlier results they concluded that the reduction of the transpiring power was due to tbe lack of water in the leaf and not to any stomatal control. Lloyd (24) found that the stomata were often opening when the water content of the plant was decreasing.…”

“…This method with the addition of more recent improvements has been frequently used (1,2,3,22,30), and appears to be very satisfactory.…”

On the Quantitative Explanation of Stomatal Transpiration

“…The same conclusion was drawn by SHREVE (1914) from similar experiments. TRELEASE and LIVINGSTON (1916), using the porometer method, found that in the course of the day the maximum of stomatal aperture was reached some hours after the maximum of transpiration, so that another mechanism seemed to play a role in regulating transpiration. KNIGHT (1917,1922) also accepted a dual influence on the transpiration rate: -the incipient drying of the cell walls would control it in case of bright weather and wide open stomata, while at low light intensities and small apertures the stomata themselves would be the main controlling factor.…”