Plant Structure and Function
What is tropism?
Tropism is the movement of a plant in response to a stimulus. The categories include:
Chemotropism—A response to chemicals by plants in which incurling of leaves may occur
Gravitropism—Formerly called geotropism, a response to gravity in which the plant moves in relation to gravity. Shoots of a plant are negatively geotropic (growing upward), while roots are positively geotropic (growing downward)
Hydrotropism—A response to water or moisture in which roots grow toward the water source
Paraheliotropism—A response by the plant leaves to avoid exposure to the sun Phototropism—A response to light in which the plant may be positively phototropic (moving toward the light source) or negatively phototropic (moving away from the light source). Main axes of shoots are usually positively phototropic, whereas roots are generally insensitive to light Thermotropism—A response to temperature by plants
Thigmotropism or haptotropism—A response to touch by the climbing organs of a plant. For example, the plant’s tendrils may curl around a support in a springlike manner