"Flats" With Sprouting Seedlings
All manner of seeds are sown in the "flats" Mr. Burbank has so perfected the method that he usually sprouts ninety-nine seeds in a hundred. The same method is used for the commmonest flowers and the rarest exotic. "Flats" growing hybrid cactuses are side by side in his greenhouse with those containing orchard fruits, and flowers of many species.
This image is from: Luther Burbank: his methods and discoveries and their practical application. Volume 3 Chapter 4