Nyctinasty is the periodic response of plant organs to the alternation of day and night, such as the opening a closing of flowers. It is caused by changes in light intensity and temperature. See also biorhythms.
Thermonasty (from the Greek thermos, 'hot') refers specifically to heat sensitivity. If we take a tulip from outside into a room 20 degrees warmer the petals will open within a few minutes; the reverse will happen of we take the tulip outside again. Many plants, such as anemone, geranium, crocus and wood sorrel can perceive very slight changes in temperature and react to them; the crocus reacts to a change of 1°F.