It is blackberry season and I just came across this amazing USDA (United States Department of Agriculture) website containing images in high resolution scans of of 7,300 fruits (mostly apples). Enjoy!

Here is an article, The collection of pomological watercolors at the United States Department of Agriculture, published in 1982 in the Journal of Botanical history by Carnegie-Mellon University. And, also, a recent article in Slate.