Label on Greenhouse "Flat"
In working on a large scale, time-saving is imperative. Mr. Burbank finds this simple method of labeling his "flats" to serve an excellent purpose. The label is easily replaced, or the penciled inscription may be erased, and a new one substituted, when the "flat" is used for another experiment.
This image is from: Luther Burbank: his methods and discoveries and their practical application. Volume 3 Chapter 8