Laura Erickson wrote about the history of the North American field guide at her blog here:
For those interested in learning more about the history of the bird guide you might want this book when it comes out:
In the Field, Among the Feathered: A History of Birders and Their Guides by Thomas R. Dunlap. Oxford University Press. Hardbound: 256 pages. Price: $34.95 U.S. DUE out in November/December 2011.