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]