Smallseed dodder (Cuscuta planiflora) gravitropism in red light and in red plus far-red

White light-grown seedlings of smallseed dodder were cyclically irradiated from above with red light for 4 h followed by red plus far-red for 4 h. Tracings of initially nearly vertical, white light-grown seedlings were made from time-lapsed video images after four cycles of red light followed by red plus far-red. Stems of seedlings cycled into red light were negatively gravitropic and stems of seedlings then cycled into red plus far-red became photoreversibly, positively gravitropic. Observations suggest gravitropic sign reversal in smallseed dodder is regulated by phytochrome.