This is a good resource for general understanding of wood. It's a huge file, take it a chapter at a time.
http://www.fpl.fs.fed.us/products/publications/several_pubs.php?grouping_id=100&header_id=p
I bought my first copy in '76. When my wife's father passed the family came across his '54 copy and it is now on my shelf, now I can click and have it for free. Pretty neat to see how it has evolved over the years.
Cool. Thx Don P.