Three Stages of Development
At the left is the original wild French plum, called the Sans Noyau-of insignificant size and practically inedible. It is almost stoneless. Mr. Burbank improved the plum by hybridizing it with cultivated varieties retaining the stoneless condition and introducing the qualities that make a commercial fruit. The central figure shows the plum at the right the same fruit as represented by its improved stoneless descendant a generation or two later.
This image is from: Luther Burbank: his methods and discoveries and their practical application. Volume 2 Chapter 4