Rapid Changes in Transpiration in Plants

Abstract

I SHOULD like to put forward a different interpretation for the experiment illustrated in Figs. 2 and 3 of the recent article in Nature under the above title¹. It may be presumed that at the start of the second part of the experiment (Fig. 3, Curve II) the leaves in the cuvette C of Fig. 2 were not flaccid or such an important fact would have been mentioned ; therefore the suction pressure in the transpiring mesophyll cells must initially have been less than the full osmotic pressure of their vacuolar sap, and this in turn must have had a value much lower than the 40 atmospheres or so exerted by the 1 M sodium chloride solution (here assumed to be at 20° C) which replaced the water in vessel B. The latter change therefore caused a considerable suction pressure gradient down the plant from the leaf mesophyll cells to the solution in B and water must have moved out of the roots into the salt solution—any increase in water permeability of the roots would only accelerate this water loss. At the same time the mesophyll cells continued to transpire, and at an enhanced rate, as shown by the curve. They must, therefore, have been losing turgor rapidly.