Fruits of the Sugar Prune
With the Splendor Prune, previously shown, Mr. Burbank had produced a nearly perfect fruit; but the fault of clinging to the tree when ripe was one that had to be overcome, and this was accomplished after years of additional experiment. The fruit that retained the good qualities of the Splendor, and accentuated them and which in addition had the quality of dropping from the tree when ripe was named the Sugar Prune.
This image is from: Luther Burbank: his methods and discoveries and their practical application. Volume 5 Chapter 4