Below is a link to The USDA Forest Products Lab Wood Handbook - a nice resource. I have seen this book for sale various places, but it is available for free download from the FPL website.http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr113.htm
The Handbook is geared toward engineering of light frame and timber structures, but there are some chapters that are useful information for puzzlemaking also. Here are several of the chapters that I have found useful for puzzles & understanding the pertinent wood behavior that goes with the puzzles:
Chapter 2 -- Structure of Wood
Chapter 3 -- Physical Properties and Moisture Relations of Wood
Chapter 9 -- Adhesive Bonding of Wood Materials
Chapter 12 -- Drying and Control of Moisture Content and Dimensional Changes
Chapter 15 -- Finishing of Wood
The finishing chapter has a nice Table 15-3 which lists the "moisture excluding effectiveness" of various finishes. Paraffin ranks the highest - which explains some of my earlier comments to some of you via e-mail. Anyway - the table gives you some idea of what finishes slow down (more or less than others) the transfer of moisture between the environment and the wood (impossible to stop this transfer, it seems).
Lots of goodies here. If you have Q's about terminology or anything, please let me know and I can help figure it out.