circumnutation

This I proved to be the case; and I was further led to a rather wide generalisation, viz., that the great and important classes of movements, excited by light, the attraction of gravity, &c., are all modified forms of the fundamental movement of circumnutation.

Circumnutation, sėr-kum-nū-tā′shun, n. a nodding or turning successively towards all points of the compass, as in the tendrils of plants.—v.i.

The changes of position of leaves and of climbing plants, and the sleep of leaves are all brought under this great principle of circumnutation.

The nature of the movement is thus a successive nodding to all the points of the compass, whence it is called by Darwin circumnutation.

Ordinary circumnutation is converted into a nyctitropic movement, firstly by an increase in its amplitude, but not to so great a degree as in the case of climbing plants, and secondly by its being rendered periodic in relation to the alternations of day and night.