Prune D'Agen Fruit
This is the French prune originally brought to California more than 50 years ago, and grown almost exclusively until the appearance of the new Burbank prunes. It is a small, sweet fruit with a tough skin, growing on a weak tree of comparatively poor bearing qualities. This prune has been used extensively by Mr. Burbank in his hybridizing experiments.
This image is from: Luther Burbank: his methods and discoveries and their practical application. Volume 5 Chapter 3