Re: Do Vines Twine Counter-Clockwise Only?

The short answer is no. However, based on the thorough observations by the French botanist, Baillaud, most plants exhibit a right-handed rotation (counterclockwise). This handedness is called chirality. The general phenomenon manifested by shoot twining is called circumnutation. This was described throughly in a book by Charles Darwin and his son Francis, The Power of Movement in Plants (1880). They didn't make a big deal about direction of movement but they showed that all plants and all parts of plants circumnutate. Also, they proposed that phototropism (response to light) and gravitropism (response to gravity) were augmentations of circumnutation. How plants do this is still unknown. Darwin proposed that it was "autonomously induced." This came to be known as the internal oscillator theory. In the 1960's the gravitropic overshoot theory explained mathematically how circumnutation could spontaneously occur as a result of forces related to gravity and growth. Recent experiments on the Space Shuttle have demonstrated that gravity is not necessary for circumnutation. It appears that we're back to 1880.

To get back to the original question of chirality, most people believe (including me until recently) that a species of plant only nutates with a specific handedness. This idea is so prevalent that recently Italian botanists described a mutant plant whose roots circumnutate left-handed (clockwise) instead of right-handed. Johnsson, a Norwegian botansist, and world authority on circumnutation, pointed out recently in a paper that many plants can change their direction of rotation while they are still growing. It's not known what causes this. The question of chirality in circumnutation is still very open.