Thigmotropism occurs due to unilateral growth inhibition. In twining and tendrilled plants, the growth rate on the side which is being touched is slower than on the side opposite the touch. The resultant growth pattern is to curl around the object which is touching the plant.

Roots also rely on touch to navigate their way through the soil. Generally, roots have a negative touch response, meaning when they feel an object, they grow away from it. This allows the roots to go through the soil with minimum resistance. Because of this behavior, roots are said to be negatively thigmotropic.

I’m tucking this new word into my vocabulary pocket for a future scrabble game.