tropizm
Tropizm, or tropism, is a directional growth response of an organism or its part toward or away from a stimulus. The response is typically structural and directional, resulting from uneven growth on different sides of the organ. Tropisms are often described as positive when growth or movement is toward the stimulus and negative when it is away from it.
In plants, tropisms are best known and studied. Major types include phototropism (growth toward light), gravitropism
Historically, experiments by Charles and Francis Darwin on coleoptiles and later work by others, including Fritz
Tropism is distinct from nastic movements, which are non-directional in relation to the stimulus, and from general