Final answer:
Most plants show positive phototropism, growing toward light, but lianas show negative phototropism after germination. This is because lianas have already established themselves in their search for light by climbing up a support structure.
Step-by-step explanation:
Phototropism is the directional bending of a plant toward or away from a light source. Most plants exhibit positive phototropism, growing toward light, because leaves and stems need light for photosynthesis. However, some lianas, or climbing plants, show negative phototropism after germination, growing away from light. This is because lianas have already established themselves in their search for light by climbing up a tree or other support structure, and growing towards light would take them away from their support.