"Three-String" Plum Fruit
On the Burbank experiment farms the plants to be saved are marked with a white strip of cloth or string. The name of this plum indicates that it has been so marked, not once, but on three occasions, a triple tribute of its value. A fruit thus honored in the Burbank orchard must have altogether exceptional merits.
This image is from: Luther Burbank: his methods and discoveries and their practical application. Volume 5 Chapter 7