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Associated word: nyctitropic. sleepwalker, n. somnambulist, noctambulist, somnambulator, somnambule. sleepwalking, n. somnambulism, somnambulation, somnambulance, noctambulism, noctambulation.

The so-called sleep or nyctitropic movements of leaves are determined by the daily alternations of light and darkness.

Although the nyctitropic movements of leaves and cotyledons are wonderfully diversified, and sometimes differ much in the species of the same genus, yet the blade is always placed in such a position at night, that its upper surface is exposed as little as possible to full radiation.

It should be premised that the nyctitropic movements of leaves are easily affected by the conditions to which the plants have been subjected.

Carl Kraus has also lately insisted** on the great influence which the quantity of water absorbed has on the periodic movements of leaves; and he believes that this cause chiefly determines the variable amount of sinking of the leaves of Polygonum convolvulus at night; and if so, their movements are not in our sense strictly nyctitropic.