  We investigate if the fluctuations of the scalar field mediating quintessence
-- the cosmon -- can play an important role in cosmology. Small fluctuations
with short wavelength behave similar to a relativistic gas. In contrast, the
contribution to the energy density from horizon size fluctuations may decrease
less rapidly than radiation. We discuss the possibility that the cosmon
fluctuations grow nonlinearly, form lumps and constitute the clustering dark
matter of the universe. Cosmon dark matter would lead to interesting
consequences for the equation of state and the coupling between quintessence
and dark matter.
