Question

1. what is an example of a positive form of thigmotropism?

roots growing laterally if there is too much resistance to them growing down
roots avoiding large rocks in the soil by growing and extending around them
mimosa plant folding its leaves when touched in an effort to keep them from being eaten
grapevine tendrils that coil around objects like sticks or trellises to stabilize them

Explanation:

Thigmotropism is a directional growth response of a plant to touch. Positive thigmotropism involves growth towards the touch - stimulus. Grapevine tendrils coiling around objects (a touch - stimulus) to stabilize the plant is an example of positive thigmotropism as the tendrils grow towards and around the object (the touch source). Roots growing laterally due to resistance is more of a response to mechanical impedance (negative geotropism in a sense, but not positive thigmotropism). Roots avoiding rocks is a growth response to an obstacle (not positive thigmotropism). Mimosa plant folding leaves is a thigmonastic (non - directional) response, not a tropism (directional growth response).

Answer:

grapevine tendrils that coil around objects like sticks or trellises to stabilize them