This paper displays a preliminary result of studying disciplinarity and interdisciplinarity based on a new source of data: doctoral dissertations. By looking into the doctoral dissertations across more than a century, this paper aims to report the overall development of disciplines and the interaction among disciplines. Preliminary results demonstrate significant increases in the number of disciplines across the 20th century and the level of interaction among disciplines. This poster focuses on the 30 highest producing disciplines and examines the dependency of these disciplines on other disciplines (where dependency is measured by the proportion of dissertations within that discipline that are also labeled with another discipline). The data reveals that science disciplines (e.g., mathematics, chemistry, and physics) bare fewer interdisciplinary features than social science and humanities disciplines and that many contemporary social science and humanities disciplines (e.g., black studies and women's studies) are highly dependent. The implications of these preliminary findings and the areas of further investigation using this dataset are proposed.