What causes dye to diffuse away from its source on an agar plate?

Dye diffuses away from its source on an agar plate primarily due to the process of diffusion, where molecules move from an area of higher concentration to an area of lower concentration in an attempt to reach equilibrium. The semi-solid nature of the agar allows for the movement of dye molecules through the gel matrix, driven by random molecular motion. Temperature, molecular size, and the concentration gradient also influence the rate and extent of diffusion.