These labels are important time-savers. Each set of holes represents a specific plant or a different type of experiment,the key to the labels being found in the record books. The upper left hand label here shown might indicate, for example, that the branch on which it is tied bears blossoms of the Sugar prune (one hole at base of label), fertilized by pollen of the Conquest stoneless prune (three holes at center of label). Such labels as this are loosely attached to the stem of the plant that has been pollenized or grafted. They are permanent, and they minimize mistakes.
This image is from: Luther Burbank: his methods and discoveries and their practical application. Volume 3 Chapter 8