Which method of grass dispersal involves physical adaptation of the plant?

The method of grass dispersal that involves a physical adaptation of the plant is the use of awns and barbs. Awns are elongated bristle-like structures that can be found attached to the seeds of certain grasses. These adaptations serve several purposes in the dispersal process.

When seeds with awns land on the ground, the awns can catch on fur, clothing, or other surfaces, effectively hitching a ride to new locations where the seeds can germinate and grow. This mechanism enhances the chances of the seed reaching a suitable environment for growth, thus facilitating the plant's spread over a wider area. Additionally, the awns may help the seeds to orient themselves for optimal germination and improve their chances of establishing a successful seedling.

Physical adaptations like awns and barbs are crucial in the evolution of grasses, as they allow for effective dispersal without reliance on external agents like animals or wind, which might not always be present. In contrast, the other options represent different dispersal mechanisms that do not involve specific structural adaptations of the plants themselves.