The good news today is that the National Agricultural Library has provided many of its historical files to the Biodiversity Heritage Library. (Read the announcement here.)
Why am I recommending you head on over & adore, too? Well, here are a few watercolors that are now available, for free, on the web, thanks to the high-quality digital scans. See if you agree!
There are also scanned documents, including historic USDA documents on organic farming (many from before 1942), and a Manual of Gardening for Bengal & Upper India, 1864 (no pictures, unfortunately).
(It's dry inside by my computer, not so much outside, though our ark is coming right along.)