Plant material
We collected branches from three to five individuals of each of four woody species varying strongly in leaf morphology and trichome depth (Table 2) growing on the UC Davis campus (Davis, CA, 35.54oN, 121.75oW), recut them under water upon return to the laboratory, and allowed them to equilibrate for at least one hour in darkness before beginning measurements. For the fifth species (Solanum lycopersicon , SOLY), we compared leaves from five plants from each of two mutant genotypes (Wo , wooly;h , hairless) in the same genetic background (known as ’Ailsa Craig’). SOLY seeds were provided by the UC Davis Tomato Genetics Resource Center. We grew SOLY plants under LED lights in the laboratory for a month before experiments.