MOST OF US are familiar with the observation that house plants placed near a window have branches that grow toward the incoming light. This response, called phototropism, is an example of how plants alter their growth patterns in response to the direction of incident radiation. This response to light is intrinsically different from light trapping by photosynthesis. In photosynthesis, plants harness light and convert it into chemical energy (see Chapters 7 and 8). In contrast, phototropism is an example of the use of light as an environmental signal. There are two major families of plant responses to light signals: the.
