This is a wonderful resource from the library of the world-renowned Missouri Botanical Garden, which I found courtesy of Richard Akerman’s Science Library Pad. From the Botanicus website:
"The problem: Digitizing, indexing, and annotating historical scientific literature is vital to future research in systematic botany, the science of the identification of plants. Like other natural history disciplines – but unlike the physical sciences – systematic botany is built upon and requires frequent reference to the literature of its past. To conduct carefully documented and authenticated research, botanists must spend weeks in library collections searching the published botanical literature for data to develop a new project or substantiate their recent observations. Comprehensive collections of botanical literature are only available in a handful of libraries, all located in North American and Europe. For botanical researchers, these library-centered literature searches, while a crucial requirement of any project, delay hypothesis development or recognition and publication of new plant discoveries. For those traveling in remote parts of North America or stationed overseas, lack of access to library resources compounds these difficulties. Further, no matter how scrupulous the search, when scientists must work manually through an array of journals and books it is impossible to be sure that all historical facts have been located and all published observations have been seen. Over 67,000 systematic botanical publications exist, but only those most recently published are in digitized form.
The solution: To improve access to scientific literature, we have created Botanicus, a freely accessible, Web-based encyclopedia of digitized 18th and 19th century botanical literature from the Missouri Botanical Garden Library. We have been digitizing materials from our library since 1995, focusing primarily on beautifully illustrated volumes from our rare book collection."