Symbols are objects, characters, figures, or colors used to represent abstract ideas or concepts.
The rushes that Alice pulls from the water in Chapter 5 represent dreams. Rushes are plans that grow in riverbeds and poke through the surface of the water. The rapid fading of the rushes’ sweet scene after being picked corresponds to the fleetingness of the memory of a dream after a person wakes up.
Tweedledum and Tweedledee tell Alice that she is only a creation of the Red King’s dream, which implies that Looking-Glass World is not a construction of Alice’s dream. The Red King becomes a divine figure who dreams up all of Alice’s adventures, fostering the idea that she does not actually have any identity or agency beyond what she is allowed in the context of the dream. The idea that we are all just aspects of the dream of a divine power comes from Bishop Berkeley, a philosopher who wrote during Carroll’s lifetime and who believed that man and the universe exist as part of God’s imagination.