Abstract: | Previous work has shown that stomata respond directly to light,but it was not clear whether the only additional response isthrough CO2, or whether some other metabolite is involved inthis response. Gas exchange experiments were done with normallypositioned and inverted leaves of Hedera helix to investigatethis problem. The macroscopic optical properties of the leavesand their anatomical structure were also studied. These experimentssnowed that there is no need to postulate the existence of amessenger other than CO2 to explain the indirect response ofstomata to light. The experiments also showed that leaf inversionaffects both stomatal conductance and photosynthesis, and highlightthe difficulties involved in the interpretation of the effectof leaf inversion on stomata when stomatal conductance measurementsare not done concurrently with measurements of CO2 flux densityand intercellular CO2 molar fraction Key words: Hedera helix, ivy, gas exchange, leaf inversion, stomatal conductance, light, CO2 flux density, photosynthesis |