Not So Good As They Look
The plum here shown was absolutely stoneless, but it was found to be too bitter to eat. Its only value was as a parent in further breeding experiments, in which the quality of stonelessness could be retained while good qualities of flesh were introduced. It will be understood that a plum may be altogether stoneless and yet retain a kernal that is viable.
This image is from: Luther Burbank: his methods and discoveries and their practical application. Volume 5 Chapter 5