The consequencies of diffusive acceleration of cosmic rays in supernova shocks propagation through an inhomogeneous interstellar medium are explored. The acceleration takes place in the hot, tenuous, intercloud gas, while nuclear collisions, leading to the production of cosmic ray secondaries, predominantly occur in those regions where the supernova shocks collide with interstellar clouds. A simple model is used to calculate the interaction of a (cosmic ray + gas) shock with a cloud, and thus determine the gross topology. Extending this to the whole system, using mean cloud sizes and space densities, allows us to calculate the secondary/primary cosmic ray abundance ratios for light and heavy nuclei.