Unlike animals, plants cannot move to more favorable locations. Instead, plants survive by adjusting their growth to their local environment. A major way this is done is by sensing the directions of environmental signals such as light and gravity. This sensory information is then used to orient the direction of growth toward or away from a stimulus in a process called a tropism. By these mechanisms, shoots grow up from the ground and into the light. This enhances photosynthesis and biomass by increasing the amount of sunlight absorbed by chlorophyll. The raised stature of the plant also promotes pollination and seed dispersal, and increases plant competitiveness.

Tropisms are different from nastic movements. Like tropisms, these plant movements are influenced by environmental cues. But the direction of a nastic movement is independent of where the signal comes from, and most such movements are...