  String theory in d dimensions has n+1=11-d parameters that may be thought of
as being inherited from the geometry of an n+1 torus which may be used to
construct the theory using dimensional reduction from eleven dimensions. We
give the precise relationship between these parameters and the expectation
values of the scalar fields that parameterise the E_{n+1} coset of the d
dimensional theory. This allows us to examine all possible limits of the
automorphic forms which occur as the coefficient functions of the higher
derivative corrections to the d dimensional type II string effective action.
