  We study an ensemble of branched polymers which are embedded on other
branched polymers. This is a toy model which allows us to study explicitly the
reaction of a statistical system on an underlying geometrical structure, a
problem of interest in the study of the interaction of matter and quantized
gravity. We find a phase transition at which the embedded polymers begin to
cover the basis polymers. At the phase transition point the susceptibility
exponent $\gamma$ takes the value 3/4 and the two-point function develops an
anomalous dimension 1/2.
