Original papers by Jack R. Edmonds referencing the P versus NP question:
Jack R. Edmonds, Paths, Trees, and Flowers, Canadian Journal of Mathematics, 17, 449-467, 1965. [PDF file].
Jack R. Edmonds, Minimum Partition of a Matroid into Independent Sets, Journal of Research of the National Bureau of Standards, 69B, 67-72, 1965. [Read Online].
Historical accounts of the development of the P versus NP question mentioning Jack R. Edmonds' contributions:
Michael Sipser, The History and Status of the P Versus NP Question, STOC '92 Proceedings of the Twenty-fourth Annual ACM Symposium on Theory of Computing, Pages 603-618, Victoria, B.C., Canada, 1992. [PDF file].
Christoph Witzgall, Ronald Boisvert, Geraldine Cheok, Saul Gass, Alan Goldman, James Lawrence, Paths, Trees and Flowers, A Century of Excellence in Measurements, Standards, and Technology: A Chronicle of Selected NBS/NIST Publications, 1901-2000, Pages 140-144, 2001. [Read Online]