Botany, Medical
Free to read here, from Project Gutenberg.
The Complete Herbal
Pharmacographia
Herbal simples approved for modern uses of cure
The Botanical Lore of the California Indians
Madame Young's Guide to Health
Histology of medicinal plants
Remarks on the Uses of some of the Bazaar Medicines and Common Medical Plants of India
Drug Plants Under Cultivation
Wild medicinal plants of the United States