Twining Motion of Vines
This video clip shows the extreme nutational movements of morning glory vines. Climbing vines need to find a suitable support on which to grow. Shortly after germinating, the young plant begins what appears to be a hunting motion in which the shoot tip rotates in a nutational movement. This swinging around of the tip is thought to help the plant bump into a support. If the shoot rubs against a support with the right shape, the rubbing induces a thigmotropic response (tropism induced by touch) and the shoot begins to curl around the support. This clip shows three morning glory plants at the stage where they have just begun “looking” for a support to climb. Vines typically show the most extreme nutational movements.
Source: ScienceTrack via Bits & Pieces