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The nature of the movement is thus a successive nodding to all the points of the compass, whence it is called by Darwin circumnutation. The movement belongs to all young growing parts of plants. The great sweeps of a twining stem, like that of the Morning-Glory, are only an increase in the size of the circle or ellipse described.
Thus the great sweeps made by the stems of the twining plants, and by the tendrils of other climbers, result from a mere increase in the amplitude of the ordinary movement of circumnutation." When a young stem of a Morning-Glory, thus revolving, comes in contact with a support, it will twist around it, unless the surface is too smooth to present any resistance to the movement of the plant.
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, etc., are all modified forms of the fundamental movement of circumnutation.
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