Plants of <i>Ipomoea quamoclit</i> L. were exposed to an 8-hour photoperiod under natural daylight, which was supplemented
with 60 W incandescent lamps to give an 8- to 24-hour day. Under photoperiods of 12 hours or less, flower buds were
initiated, while the period from bud formation to flowering was shortened in plants grown under a 12-hour photoperiod.
Photoperiods of 12 hours or less had no effect on plant height and number of nodes. The present results suggest that
Ipomoea <i>quamoclit</i> L. is a short-day plant.