Phototropism is irectional growth in which the direction of growth is determined by the direction of the light source. In other words, it is the growth and response to a light stimuli. Phototropism is most often observed in plants, but can also occur in other organisms such as fungi. Phototropism is one of the many plant tropisms or movements which respond to external stimuli. Growth towards a light source is a positive phototropism, while growth away from light is called negative phototropism (or Skototropism). Most plant shoots exhibit positive phototropism, while roots usually exhibit negative phototropism, although gravitropism may play a larger role in root behavior and growth. Some vine shoot tips exhibit negative phototropism, which allows them to grow towards dark, solid objects and climb them.