The Collaborative International Dictionary
Nyctitropism \Nyc*tit"ro*pism\, n. [From Gr. ny`x, nykto`s, night + ? to turn.] (Plant Physiol.) The tendency of certain plant organs, as leaves, to assume special ``sleeping'' positions or make curvatures under the influence of darkness. It is well illustrated in the leaflets of clover and other leguminous plants.
Wiktionary
n. (context botany English) (alternative namenyctinasty)
Usage examples of "nyctitropism".
The sleep or nyctitropism of leaves is a large subject, and we think that the most convenient plan will be first to give a brief account of the position which leaves assume at night, and of the advantages apparently thus gained.
On this view of the origin of nyctitropism we can understand how it is that a few plants, widely distributed throughout the Vascular series, have been able to acquire the habit of placing the blades of their leaves vertically at night, that is, of sleeping,--a fact otherwise inexplicable.
From the facts and considerations now advanced we may conclude that nyctitropism, or the sleep of leaves [page 413] and cotyledons, is merely a modification of their ordinary circumnutating movement, regulated in its period and amplitude by the alternations of light and darkness.