Tropisms are usually named for the stimulus involved (for example, a phototropism is a reaction to light) and may be either positive (towards the stimulus) or negative (away from the stimulus). Four Types of Tropism - 1. Phototropism: It is the Directional Movement or Orientation of the Plant Part.in response to Light Stimulus. If the Plant Part Moves Towards the Light it is Called Positive Phototropism If the Plant Part Moves away from the Light it is Called Negative Phototropism 2. Geotropism: