Scientists investigated the effect of abscisic acid (ABA) on reducing water loss in plants. The scientists predicted that ABA, as well as stimulating stomatal closure, also reduces water loss in plants in other ways. The scientists used a mutant variety of thale cress, Arabidopsis thaliana, that has stomata that do not respond to ABA. When ABA is present, the stomata of the mutant variety remain open. The scientists sprayed different concentrations of ABA on the leaves of the mutant variety and measured the transpiration rates of the plants. The results are shown in Fig. 2.1. [Figure 2.1]