Representation of a natural number by positive binary quadratic forms of a given discriminant

Consider a representative system of the positive, integral binary quadratic forms of a given negative fundamental discriminant. A formula for the number of ways a positive integer may be represented by the various forms of such a system was firts given by KRONEKCER in 1885; although this result plays an important role in some parts of analytic number theory, no simple proof can be found in easily accessible literature. The present paper provides a short and elementary proof.