1. Plant hormones

2. Hormones from Gr. to excite
natural chemical messengers transported to target cells
minute concentrations = substantial change
growth regulators

3. Plants respond to stimuli

4. Plant hormones coordinate growth, development and responses to stimuli
Tropisms
growth responses
organs curve towards (+) or away from (-) a stimulus
ex. phototropism, thigmotropism, gravitropism

5. Studies on phototropism
towards or away from light
differential growth of cells on opposite sides of a shoot or coleoptile
cells on darker side elongate faster than those on the light side
experiments by Darwin and son and FW Went
due to auxin distributions

6. Went experiment