  Any planar graph has a crossing-free straight-line drawing in the plane. A
simultaneous geometric embedding of two n-vertex graphs is a straight-line
drawing of both graphs on a common set of n points, such that the edges withing
each individual graph do not cross. We consider simultaneous embeddings of two
labeled trees, with predescribed vertex correspondences, and present an
instance of such a pair that cannot be embedded. Further we provide an example
of a planar graph that cannot be embedded together with a path when vertex
correspondences are given.
