The ruthenate compounds, Gd_2–zCe _z Sr₂Cu₂RuO₁₀, GdSr₂Cu₂RuO₈, and doped Sr₂YRuO₆, all superconduct in their SrO layers, which is why they have almost the same 49 K onset temperatures for superconductivity. The sister compound Ba₂GdRuO₆, either doped or not, does not superconduct, because L = 0, J 0 Gd breaks pairs and destroys superconductivity in the potentially superconducting BaO layers. High-temperature superconductivity resides in the SrO or BaO layers, or in interstitial-oxygen regions of the crystal, not in the cuprate-planes.