The Differential Transpiration Porometer

The construction and testing of a new differential transpirationporometer for stomatal measurements are described. The principleinvolved is explained, and the mathematical theory is dealtwith in an appendix. As a result of experiments comparing the new instrument's readingswith those obtained with a Wheatstone bridge porometer, a relationbetween diffusive conductance and viscous flow conductance isfound; in the case of wheat stomata this approaches a cubicrelation and in the case of Talinum triangulare a quadraticone.