Schematic representation of a supernova exploding in the wind of its parent star. The star of initial mass M_∗ explodes with a mass M_Exp, i.e. it has lost a mass M_wind = M_∗ − M_Exp. The most massive stars become WR stars and their wind expels not only the H-envelope (of mass M_Env, with composition similar to that of the ISM) but also nuclearly processed layers, of mass M_Proc, i.e. M_Wind = M_Env + M_Proc, where M_Proc = M_HeC − M_Exp and M_HeC is the mass of the (H-exhausted) He-core. The star leaves a remnant (neutron star or black hole) of mass M_Rem; the mass ejected in the SN explosion is M_Ej = M_Exp − M_Rem. Efficient GCR acceleration presumably starts at the beginning of the ST phase, when a mass M_S1 ~ M_Ej is swept up in front of the SN shock wave (which is indicated by arrows).