Movement of plant parts in response to a unidirectional light stimulus is called phototropism. Some parts of the plant e.g., stem moves towards the source of light. These organs are called positively phototropic. Some other organs e.g., roots move away from light and they are called negatively phototropic. In a plant, leaves are placed at right angles, to the direction of light source, and are called transversely phototropic or plageo-phototropic. The curvature of the stem tip is explained by the unequal distribution of Auxin on either side of the light-induced stem.
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Movement of plant parts in response to a unidirectional light stimulus is called phototropism. Some parts of the plant e.g., stem moves towards the source of light. These organs are called positively phototropic. Some other organs e.g., roots move away from light and they are called negatively phototropic. In a plant, leaves are placed at right angles, to the direction of light source, and are called transversely phototropic or plageo-phototropic. The curvature of the stem tip is explained by the unequal distribution of Auxin on either side of the light-induced stem.