Karen just sent me a link to www.botanicus.org with regards to sourcing imagery for work we are doing on the Grizedale Arts website, for visual reference. It's full of scans of out of copyright books from the Missouri Botanical Garden Library, and it's full of wonderful things.
Botanicus is a freely accessible, Web-based encyclopedia of historic botanical literature from the Missouri Botanical Garden Library. Botanicus is made possible through support from the W.M. Keck Foundation and the Andrew W. Mellon Foundation.