Alf Hornborg says many useful things in his article, “Ecosystems and World Systems: Accumulation as an Ecological Process.” His effort to “ground the notion of capital accumulation in the physical realities of ecology and thermodynamics” is a much-needed corrective to nature-blind studies of capitalism. At a more paradigmatic level, his dismay at the “analytical disjuncture of ecology and economics” in modern social science is right on target (1998: 169). Yet, despite the article’s laudable intent, Hornborg goes astray by imputing to Marx a focus on labor that excludes the “physical realities” of labor reproduction, world trade, or imperialism. Hornborg is right to urge a synthesis of ecological and economic studies, but wrong in his call to “supplement” the labor theory of value with a “resource-oriented…concept of exploitation” (1998: 173). Even if Marx did not grapple with a global ecological crisis of contemporary standards, he was remarkably sensitive to ecological processes as they shaped, and were shaped by, capital accumulation; indeed, Marx studied intensively the works of the leading soil chemists of his day, foremost among them Justus von Liebig. Particularly in the ?rst and third volumes of Capital, Marx provides a compelling framework for comprehending the nature-society dialectic under capitalism.