Classic texts: Scudder's Materia Medica, 1898: Alteratives.
Classic texts: Eli Jones' Definite Medication, 1911.
Classic texts: Ellingwood 1910.
Classic texts: Thomas 1907.
Classic texts: Journals: NEMAQ 1915-1916.
Classic texts: Journals: AJP 1881.
Henriette's herbal is one of the oldest and largest herbal medicine sites on the net. It's been online since 1995, and is run by Henriette Kress, a herbalist in Helsinki, Finland.
Plant Healer Magazine: Very relevant to the practitioner.
http://www.henriettes-herb.com - Copyright 1995–2015 Henriette Kress.