The pressure bomb (4) is used to measure leaf water potential (IY(1)) of cotton in a variety of experiments. Sample handling can significantly affect results and their interpretation. Turner (5) showed that exposure of an excised cotton leaf to the atmosphere for as little as 10 to 30 seconds can reduce by approximately 3 to 5 bars with the magnitude of the decrease proportional to stomatal conductance and transpiration rate. The error can be minimized or eliminated by inserting the leaf into a plastic bag immediately before excising the leaf, expelling air from the bag and sealing the leaf blade and petiole in the bag after excision until analysis (1, 2, 5, 6).

Wenkert et al. (6) measured a 10 to 15 C increase in chamber gas temperature due to adiabatic warming during pressurization of the chamber, increasing the potential for transpiration loss during pressurization. They reported that protecting the leaf in a plastic bag during the pressurization could reduce the water loss associated with the temperature increase.