Studies on the Transpiring Power of Plants as Indicated by the Method of Standardized Hygrometric Paper

Abstract

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The Interrelations of Stomatal Aperture, Leaf Water-content, and Transpiration Rate

“…It appears therefore from the results of these experiments that in plants under quite ordinary conditions, changes of stomatal aperture and transpiration do not necessarily run parallel. Darwin (9) claims a much closer correlation between these two functions than has been obtained in the present work, but Darwin made no attempt to control his experimental conditions, 1 and most of his transpiration measurements were based upon readings of absorption by the plant from a potometer, uncontrolled by weighing; although, as has been frequently shown, absorption is not by any means necessarily the same as transpiration. The differences between the two can be large enough to influence the transpiration rate without causing any obvious change in the turgor of the leaf, as has been demonstrated by many of the above experiments, so that the fact that a plant is not flaccid is no assurance that its rate of absorption is equal to its rate of transpiration.…”

“…The existence of this inhibiting factor has been demonstrated in various plants by Shreve (21) and Giddings (12) in a similar manner, and also by Bakke (1), Trelease and Livingston (22), and Bakke and Livingston (2), using the hygrometric paper method. In addition to this ' early maximum' of transpiring power, a secondary maximum has also been found by Bakke (1), Shreve (21), and by Bakke and Livingston (2) in various plants.…”

Recent Work on Transpiration

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

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

“…For the tests with cobalt chloride paper, essentially the same method was used as that described by Livingston (8) and recently employed by Bakke (1). Small squares of thin filter paper, impregnated with cobalt chloride, were dried for a few seconds over a thin metal plate, heated by an alcohol lamp, and immediately applied, by means of little glass clips, to the lower surface of the leaf to be tested.…”

“…The foliar characteristic here considered may be directly determined in several ways. (1) The entire aerial part of a plant, or an entire branch, may be enclosed in a chamber and the rate of transpiration may be measured for any given set of conditions (temperature, humidity, wind velocity, etc.). If the surrounding conditions remain the same and the rate of water-loss varies from period to period these variations must be due to internal conditions and the different observed rates should be proportional to the various degrees of transpiring power.…”