Wood toxicity, allergies and database.
A comprehensive guide with more information than anyone is likely to need but well worth the trouble of referencing woods that you are likely to use. It is written in a no nonsense and understandable way.
Also have a look at some of the articles past the database.
Credits are to Eric Meier who has published a book called WOOD full of information.
On our clubs doorstep at unit 49B
Supplies high class pen kits, pen blanks, woodturning blanks, Chestnut finishes etc