The dissertation departs from the premise that the materiality of living organisms, usually studied by the biological sciences, is essential to the social sciences in order to understand how nature is transformed by, and also transforms the distinctly different materiality of social relations. Agricultural plants are an excellent illustration of this, because how societies produce with them coincides materially with how plants reproduce, i.e., with their various living processes. Despite these deep connections, the disciplinary divide between the natural and the social sciences has generated no conceptual tools for studying the materiality of living nature in the social sciences. To address this problem, the dissertation develops an original analytic framework that captures the transformations in living organisms through spatiotemporal categories. These are used to analyze the transformation of agricultural plants in three major contexts: Peasant farming, Mendelian genetics and molecular genetics. Spatiality and temporality serve as research tools for approaching the research material, consisting of scientific papers, handbooks and government documents that document the transformation of agricultural plants, spanning three centuries. The spatiotemporal concepts are shown to be versatile categories, appropriate for understanding the transformations in living nature, from molecules to agroecosystems. Moreover, they are also suitable for describing social processes, in particular the practices and strategies through which peasant farmers on the one hand, and scientists on the other, have transformed plants. The spatiotemporal categories therefore result in a common perspective for showing specific mechanisms that bridge societal relations and non-social materialities. Significant insights are gained about society's relationship to agricultural plants by specifying how - rather than only recognizing that - the materiality of living plants shapes and is shaped by societal relations. These include the important role of recurring material forms such as plant seeds, creating a hiatus in the transformation of an otherwise perpetually changing materiality that results in a `fulcrum' to their transformation; the spatiotemporal stabilization of plants as a material basis for dominant forms of organizing production in various periods; or the consequences associated with practical redefinitions of living processes that abstract widely from how plant materiality has been reproduced historically. The long-term perspective used to study the transformation of agriculture is also particularly useful for understanding contemporary transformations through molecular techniques beyond plants. Of particular interest is the `fluid' relationship between human labor and the living processes of microorganisms for their potential to transform the materiality of contemporary production.