Final answer:
Thigmotropism is a plant's response to touch, and a positive form of thigmotropism is when a plant responds by coiling around an object for support, like the tendrils of a grapevine coiling around a trellis.
Step-by-step explanation:
Positive Form of Thigmotropism
A classic example of a positive form of thigmotropism is the coiling of tendrils in plants. Tendrils are specialized structures that help climbing plants attach themselves to supports and grow upward. When a tendril comes into contact with a solid object, it triggers a response that causes the tendril to coil around the object, providing support for the plant.
For instance, a grapevine uses thigmotropism to coil its tendrils around a trellis for support. As the tendril touches the trellis, the cells on the side of the tendril contacting the trellis elongate and grow faster than the cells on the opposite side. This differential growth causes the tendril to curve and eventually coil around the trellis, allowing the grapevine to climb and reach sunlight for photosynthesis.
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