He found that thigmotropism is a stronger plant response than geotropism. His experiment contrasted the response of a vertical bean root to gravity and to touch. He found that the plant defied it's gravitational response in order to fulfill its thigmotropic response. Later experiments proved that the thigmotropic response is possibly the strongest tropic response in plants. This is for good reason.
Thigmotropic responses can take the form of everythng from a slight shiver to a big chomp.
Some plants use this response to eat insects alive. Others practically conquer buildings with their curling tendrils. Thigmotropism is the closest a plant comes to imitating a typical mammalian response to physical stimuli. Not much is known of the cause of thigmotropic responses. Differential growth refers to the reaction that takes place in the side of a plant stem opposite the touching object.